Unexpected Gameplay Change

""Due to mandatory scheduled maintenance, the appropriate chamber for this testing sequence is currently unavailable. It has been replaced with a live-fire course designed for military androids. The Enrichment Center apologizes for the inconvenience and wishes you the best of luck.""

- GLaDOS, Portal

You know the feeling. You've been ruthlessly blasting through enemies with a machine gun for the past several hours, but suddenly your weapons are confiscated, and you're now forced to maneuver your way through the rest of the level stealthily while remaining in the shadows. Or you're playing a platforming game and you're forced to enter a dirtbike race in order to acquire a Plot Coupon.

You've just encountered an Unexpected Gameplay Change.

Such changes can add welcome variety to gameplay, but sometimes these (usually brief) segments are poorly implemented and only serve to disrupt the otherwise genial flow of the game. They hurt somewhat less when they're presented as genuine mini-games that you can practice or skip at your own discretion, such as in a Wide Open Sandbox, but heaven forbid if they're required for Hundred-Percent Completion, or, worse, part of the main game. In this case they may become Scrappy Levels.

This can often be a form of Fake Difficulty, and is occasionally a symptom of Disappointing Last Level.

Common forms include:
 * Breaking Out
 * Racing Mini Game
 * Stealth Based Mission
 * Unexpected Shmup Level

If used too much, it becomes Gameplay Roulette.

For an Expected Gameplay Change, see Bonus Stage. When this happens to the plot of a game (or any other media) it's a Halfway Plot Switch, Genre Shift, or Out-of-Genre Experience.

Action Adventure

 * The stealth portions in The Legend of Zelda Ocarina of Time and subsequent games.
 * Some minigames also count, if they are required to progress in the game.
 * Two sections in the Game Of The Film of Batman Begins had you suddenly driving the Tumbler. But anything involving the Tumber falls under Rule of Cool, so that's okay.
 * The Adventures of Batman and Robin, from animated series fame, had after several platforming levels where you beat up random thugs, suddenly you driving the Batmobile in a car chase with Two-Face. It's also it's resident Scrappy Level.
 * While you would expect a lightcycle race or two in the video game Tron 2.0, they show up in some strange places at the end.
 * The Super Nintendo Jurassic Park game (not to be confused with games of that name for other platforms) is an overhead action/adventure game outdoors and a first-person shooter indoors. Oddly enough, the first-person shooter segments were almost trivially easy, whereas the outdoor segments could be difficult at times, what with the enemies abruptly jumping out from under nearby foliage.
 * Beyond Good and Evil features, in addition to the primary puzzle-solving and stealth-based gameplay, several tracks' worth of hovercraft racing. (Luckily, you only have to enter one race to beat the game, and you don't even have to win it, just find the hidden passageway on the racetrack.) And the first and last dungeons are action and puzzle-oriented, while the second and third (but moreso the third) are stealth-oriented. Also, the fight against the penultimate boss is a shoot-em-up.
 * Monster Rancher Evo gets shades of this from the fandom, seeing as it toned the monster-raising simulation bits down and turned up the RPG-like customization of the games.
 * In order to beat the Hell Temple in La-Mulana, the player must get over 120,000 points in a Gradius clone. It may be the cruelest thing the game does to the player, and that's saying something.
 * You make an entry for La-Mulana in the Unexpected Gameplay Change article, and THAT'S all you choose to mention? The real contender here is the other minigame, Mukimuki SD: Memorial. When you activate it, you'll find that it appears to be a dating sim, of all things...but then, suddenly, with almost an audible * POP*, the girl turns into a feminist Snatcher, the mascot of the game, METAL FISH MSX 3 TURBO R PLUS, appears, and you begin dueling the girl in a parody of the game Snatcher. It's an Unexpected Gameplay Change inside an Unexpected Gameplay Change!!
 * Uncharted Drakes Fortune is, for the most part, a bright, fun, and adventurous puzzle/action game. Then you get to the, where the genre takes a trip down survival horror lane. Environments become dark, claustrophobic hallways, enemies are fast and things get much harder.
 * To elaborate on why this is so effective, up until 3/4ths through the game, there has been no indication (aside from some light foreshadowing that you probably didn't put too much stock in) that the last act would take...that particular direction. Up to that point, ALL the enemies you've fought have been bread-and-butter humans, whom you engage in duck-and-cover gunfights inspired by the Gears of War style. The are the first enemy in the game who will barrel straight at you, and their claws will kill you quite quickly if you get hung up on something, even on Easy. You might not have even realized that Nate can run and fire without needing to stop and aim before this point, because with the calculated, behind-cover fight style of the rest of the game, you never really had hard need for it. Here, you do: the  force you to shift your entire fight stye. The mood that the  evokes is similar to the "cut the power in the alien base" segments of the Metroid Prime trilogy. The difference being that Samus is essentially wearing a tank and Nathan Drake goes down from a few slashes.
 * In Famous had the side missions where you had to follow a Mad Bomber around without being seen until he put down his package, at which point you retrieved it. And you couldn't kill him, you just had to sneak around and hope you stayed in sight, because if you lost him you had ten seconds to find him, so sometimes you had to jump from the rooftops and try to stay undercover. Sometimes it was a real pleasure finally getting to blow him up at the end.
 * Brutal Legend's demo depicted it as a third-person hack-and-slash action sort of game. Granted, everything in the demo is there, but it quickly devolves (or evolves, depending on your viewpoint) into a unit-commanding massive RTS game for the rest of it.
 * While Nie R itself had what would be considered unusual additions (including Bullet Hell style bosses and enemies) the developers really went out of their way when they included a Text Adventure as part of the main plot.
 * Another World threw in a tank battle near the end of the game, where you had to guess the right sequence of buttons to win.

Action Game

 * The original Devil May Cry was chastised by fans for throwing an unexpected 3D Shoot'Em Up level into the mix towards the end of the game, when you . Apparently, it stuck, seeing as it hasn't been repeated in any of the sequels.
 * There was also.
 * An annoying, poorly designed jumping puzzle disrupts level 17 of Devil May Cry 3.
 * Devil May Cry 4 had not one, but two instances of an incredibly frustrating dice game. Dante just says fuck that and cuts the die in half rather than bother doing it.
 * In between the free-roaming slaughter-fest stages, MadWorld had 2 levels where you had to ride down the highway on a motorbike beating the crap out of mooks on the way to the boss. In the second of those, you fight the boss while still on the bike.
 * Bayonetta has two missions like this, one on a bike, the other on a missile, the bike mission plays like your standard driving level (minus the scrappiness, as long as you keep on the right side of the road), the second one is a homage to Space Harrier.
 * Mafia, a story-driven action-adventure game, has a racecar section which must be won in order to advance. The whole section is loathed not only because of the gameplay change, but also because the game is set in the 1930's and therefore these cars aren't exactly the easiest to drive. Rubberband AI certainly doesn't help.
 * It also had a crate stacking sequence.
 * At least you got to crank down the difficulty for that, and it's really not that much different from all the high speed chases you routinely get into. The sniper mission, however, could really throw you for a loop. From massive shootouts with bullets flying everywhere in a small space to being able to take one, maybe two shots at a distant target with a very primitive sniper rifle with the view constantly shaking. That one could take a bunch of tries.
 * When you confront the Chief of Police in Stubbs The Zombie, he tries to make good on his threat to dance on Stubbs' grave... by challenging him to a dance-off, which takes the form of a Simon-esque rhythm minigame.
 * ROM Check Fail is nothing but this. It randomly chooses a player character, targets/enemies, along with expected gameplay and behavior of both and mashes them together into twenty mind twisting levels
 * The River staqe in Adventures of Tom Sawyer for the NES is an overhead Auto Scrolling Level, and the Boss Battle of the Bubbly Clouds level is an Unexpected Shmup Level, where you ride a cloud that shoots hailstones, against a heavily-armed zeppelin.
 * Gunstar Super Heroes for the Game Boy Advance did this as well. Most of the game is a beat-em-up with little variation, however a top-down shooting stage is suddenly put in on the 2nd Moon and on any difficulty higher than easy it essentially becomes a Luck-Based Mission and That One Level due to the ridiculous damage you take from projectiles. The original version on the Sega Genesis did this as well, placing a space shooter stage into the game towards the end which also carried into the sequel (albeit the space shooter was far easier).
 * The first Lego Star Wars game had three vehicle levels (Podracing, gunships blowing stuff up on Geonosis, space battle over Coruscant) which were all partly different between each other and having gameplaywise nothing to do with the platforming/action part. It got better. Vehicle levels are now of the same standard and no longer have own rules for every level.
 * Stage 4 in Contra III, the first half of which is an auto scrolling ride on a jetbike, the second half of which has you hanging from missiles. These concepts carried over into most later games.
 * The infamous swimming level in Teenage Mutant Ninja Turtles.
 * Shadows of the Empire does this so much, it's almost expected. You have a total of four different vehicle modes, including one as a gunner of a ship you later pilot in the last level. This is within ten levels.
 * Journey to Silius's last stage is unexpectedly an Auto Scrolling Level, which greatly adds to the difficulty.
 * Raid 2020, by the kings of unlicensed garbage, Sachen and Color Dreams, has an unexpected gameplay change to a boat shooter in the second level, and a space shooter in the fourth.
 * Asura's Wrath is a subversion, in that all the random gameplay changes through the game between several different styles is an intentional version of the principle behind the trope, in that it's meant to keep you on your toes. None of them feel taacked on either, like a lot of other examples of this trope.

Adventure Game

 * The insertion of action elements (sometimes called "twitch scenes") into Adventure Games became increasingly common through the 1990s, as developers began to think that players would be attracted by them. The interactive movie game based on The X-Files turned briefly into a Rail Shooter, Dreamfall: The Longest Journey includes a number of combat scenes, etc. "Purist" adventure game enthusiasts decry the shift, firstly because they see it as a "dumbing down" of the genre, and secondly, because adventure game developers are, on the whole, not very good at writing action sequences. Or at least, not with an interface horribly unsuited to quick reactions. It's very very easy for those action sequences to become That One Sidequest.
 * Sierra was particularly infamous for this. Far too many of their games have action sequences, many of which poorly written and frustrating. Most of the time they were skippable in some way (except for the poker sequences, only possible through massive Save Scumming), but Hundred-Percent Completion was forfeit. Conquests of the Longbow, for example, had an "arcade difficulty" slider in the options. Sierra developers were sadist like that.
 * Space Quest: Examples include the landspeeder/skimmer sequence in the first game and remake, Astro Chicken and the Humongous Mecha Final Boss battle of III, and the burger-making minigame in IV.
 * So, so many Sierra games also have pointless gambling simulations shoehorned in. It worked kind of well in the vice-themed worlds of Leisure Suit Larry, but that was about it.
 * This may be due to their dabbling in card game software with the Hoyle's Official Book of Games series in the late 80's.
 * The remake of Police Quest at least allowed you to skip the poker bit.
 * The So Average Its Okay adventure game Hopkins F.B.I. had a First-Person Shooter section near the end of the game. It had Doom's mechanics, but a millionth of the fun.
 * Similarly, the even less remarkable videogame Evidence.
 * In the game Fahrenheit (2005 video game), you play the role of Lucas Kane, who was possessed and forced to commit murder. You play through the game mostly by interacting with a context sensitive environment and moving analog sticks to on-screen prompts to determine the outcome of movie-like cut-scenes. In two chapters of the game, you are forced to look back into events in Lucas' past as a child, living in a military base, where he must stealthily sneak past guards and spotlights. The game engine simply wasn't built to handle a Stealth Based Mission like this, as the camera is terribly restrictive, and the player is forced to react to obscure prompts to find the single proper path, instead.
 * The game also featured a brief, completely plot-irrelevant target range sequence.
 * Quantic Dream's previous game, The Nomad Soul, also had a significant Genre Shift towards first person shooting action, and more worrisome, towards beat'em up. None of the segments were particularly good, although some sequences were optional. Woe be to you if you reach the dramatically linear third act of the game without as many medikits as you can buy, however. No going back, and no purchasing more.
 * Adventure game Future Wars changes, right at the end, to a lengthy shooting sequence and an even lengthier run-through-the-maze sequence. It kind of felt like they didn't even bother to think up puzzles for the ending.
 * At least they were in line with the deadend-filled, rigidly linear and extremely punishing rest of the game.
 * Missing: Since January had a number of these, turning from a puzzle game to minigames. Some were good (minigolf, the cube game), other annoying (shooting parasites off of flowers, navigating a torch around holes) but all became tedious.
 * A few LucasArts adventure games had these (and arguably could have done without them). Curse of Monkey Island had ship combat, Full Throttle had motorbike fights, and Indiana Jones and the Fate of Atlantis had several, including fistfights, car chases and flying a hot air balloon. The game Indiana Jones and The Last Crusade also featured fistfights and flying a biplane.
 * The fistfights arguably weren't too unexpected. I mean, it's Indy. And Nazis! What's he gonna do, debate them?
 * Sell them fine leather jackets!
 * Both fistfights and a biplane flight occur in The Last Crusade. Including them in the video game is kind of a given. Genre shift, yes. Unexpected, no. Also In Fate of Atlantis you are presented with three choices midgame, options are solo mode, cooperative, or action, so again not that unexpected.
 * They would be unexpected if you were used to other LucasArts adventure games, which held strictly to the point-and-click interface. The Secret of Monkey Island, for instance, had sword fights, but the player won them by choosing insults for Guybrush to spout in the midst of them. Having actual combat be a key gameplay mechanic does come as a surprise, regardless of what was in the movie.
 * At the end of the second episode of Strong Bads Cool Game for Attractive People, the game switches from a click-and-point adventure to a turn-based strategy game.
 * Also, the penultimate mini-game of the fifth episode is . The final mini-game.
 * The first Dune game started off as an adventure game, then eventually turned into a strategy game for the remainder.
 * An example of gameplay change done right would be the arcade-style mashfests in Cyberflix's two games, Dust: A Tale of the Wired West and Titanic: Adventure out of Time. They're a complete 180 from the point-and-click gameplay of these adventure games, but not only are they pretty easy, there's no penalty for failing (other then missing out on one or two insignificant pieces of dialogue). The game will proceed exactly as if you'd succeeded.
 * The Sam and Max games were Point And Click Games (excepting Minigames), until Episode 3 of The Devil's Playhouse, which is an Ace Attorney-style Visual Novel. For the first part, anyway.
 * Mission Critical is a fairly well-done adventure game about a man who wakes up alone on a spaceship in the middle of a crisis and must resolve several immediate issues as well as uncover the backstory. Halfway through the game, the player has to connect to the ship's tactical system, at which point it turns into a Real Time Strategy (or Turn-Based Strategy, depending on your abuse of pauses), where the player has to destroy the opponent's capital ship(s) while defending his own. The end of the game does this as well.
 * The Maze Runner sequence in the Selenetic Age of Myst, which requires you to learn the sound cues from the Mechanical Age's Fortress Rotation Simulator to find the correct path. (Lessened somewhat by it being able to learn the cues in the maze, without going to Mechanical)
 * A couple of the Nancy Drew games throw in a chase scene at the conclusion, and a couple have rather tedious maze mini-games that are quite a departure from the series' usual brain-teaser style of Solve the Soup Cans.

Beat Em Up

 * God Hand has a jumping puzzle towards the end. Playing the game for 30 seconds will show you how inane this is.
 * Stylistic Suck controls and Platform Hell do not go together. Then again, Stylistic Suck...
 * The platform jumping areas in the NES versions of Double Dragon games. Mission 6 of the second game has a Mega Man style Temporary Platform sequence. And there's the hallway in the Temple of Doom in most versions of the first game where you have to navigate a Death Course of Smashing Hallway Traps of Doom and Spikes of Doom.
 * The Adventures of Bayou Billy was probably one of the first examples of this although it might not have been all that unexpected. The game was mostly a side-scrolling early Beat'Em Up in the vein of Double Dragon. There was still the odd driving levels and a Shoot'Em Up level where you had the option to use the Zapper light gun in place of the regular controller.
 * Streets of Rage 3 originally intended to have motorcycle and aquascooter sections, evidenced by pre-release screenshots. Streets of Rage Remake managed to include them, however.

Driving Game

 * The boat sequences in the original Spy Hunter.
 * In Super Spy Hunter, the fourth stage is an autoscrolling aerial highway where you freefall several times, and the fifth stage is a boat sequence for the first half, and a jet plane Shoot'Em Up for the second half.
 * Driver had a mission where you had to deliver a crate of explosives in a pickup truck. Too many bumps, and it blows.

Edutainment Game

 * Oregon Trail was largely a text-and-pictures wagon trail simulator, but included a hunting scene in which the player had to go out and shoot dinner in a manner reminiscent of the arcade shooter games of that era. Not to mention the rafting down the Columbia River, which was necessary if you didn't have enough money for the Barlow Toll Road and made more difficult by the fact that the only practice you got came only after the requisite hour of play to get to the end.

Fighting Game

 * In Super Smash Bros Brawl, Snake's final smash has you shooting grenades at the players like a third-person shooter.
 * To say nothing of the Subspace Emissary, of course.
 * Soul Blade goes from 3D fighting game to first person during Mitsurugi's ending: You have to fight Teppou Hei wielding Tanegashima (a primitive firearm) from a first-person view.
 * Then again it's less of a fight and more of a "sidestep left twice in a rapid succession, mash forward, press any button, win".
 * Soul Calibur III has shades of this in its Chronicles of the Sword mode, which arranges the fights on an RTS-style map and implements RPG levelling, while individual encounters are resolved in the traditional 3D-fighter-with-weapons style. The combination of AI that really only knows how to Zerg Rush, bizarre arena effects, and the fact that the enemies will always be at least five levels higher than your main character can lead to moments of frustration.
 * The Fighting Game based off of the third part of Jo Jos Bizarre Adventure had this in the form of N'Dool, whose Stand controlled water. When playing as one of the good guys, the game shifts from a fighting game into a side scroller game, wherein you must avoid various water hazards. It's difficult at best, though once you've reached N'Dool, all you gotta do is punch him once, since he is blind and therefore he can't fight back.
 * The Playstation port of the game had a "Super Story Mode" to include an event for every antagonist the party faced in the original manga. Some were like N'Dool and incorporated part of the "fighting genre" controls into an action sequence, but there were also events that were entirely different genres. Some were used several times, like incorporating quick time events into narratives of the chapter. Other genres are only used once, like the Lovers stage being a shoot-em-up.
 * The story mode gameplay of Godzilla: Save The Earth has you unexpectedly have a rail shooter battle against Ebirah if you play as Godzilla 2000.
 * Likewise, playing the story mode in hard mode as M.O.G.U.E.R.A has you fight a rail shooter battle against
 * The Outfoxies, an arcade one-on-one multi-platform fighting game (like a darkly humorous Smash Bros.) has a gameplay change on the last level. Instead of another one-on-one duel, you start off outside a seemingly empty mansion. Unsurprisingly, the mansion is booby-trapped.

First Person Shooter

 * If often appears that every First Person Shooter is forced by law to have a Jet Set Willy interlude where you have to put up your guns and bounce around rising and falling platforms and moving conveyer belts.
 * In the last third of Marathon 2: Durandal, you're unexpectedly sent from assaulting the enemy's strongholds to missions set in allied bases, populated with friendly characters ("Bobs"). The stated goal was to defend the bases from invading aliens and to sniff out the evil clone Bobs, which explode on approach.
 * Although it wasn't necessarily a genre shift. The first such level is called "God will sort the dead". Guess why. Another hint? A hidden message in another level (only visible via map editor) asks the question: "Q: What's the difference between a good Bob and a bad Bob? A: Good Bob?". Pure sadism.
 * More hidden text from the original game's BOB-heavy level, The Rose: "BOB jam? Apply grenades liberally!" Saving BOBs in this series is really more of a Self-Imposed Challenge.
 * Time Splitters: Future Perfect - mid-level/mid-game, there's a good portion of the level dedicated to solving a puzzle [similar to Slime Tube or whatever it was called] to get Cortez past security doors.
 * Happens in Star Wars: Jedi Knight II, when suddenly the main character must sneak around an Imperial base without being seen, or the Stormtroopers will rush and hit an alarm button and summon an entire garrison of Stormtroopers, who will arrest you. This would be at least understandable in the early levels when you're without Force powers (or have very weak versions), but it comes late in the game when you're an unstoppable Jedi of Death and a garrison of Stormtroopers is about as threatening as a garrison of kittens.
 * And during the vehicle sequences.
 * The stealth mission can be made more like the rest of the game (and therefore more fun) if you can get to the alarm button before any troopers can, since they need to physically hit the button to actually catch you - it's pretty hard for them to do so when said unstoppable Jedi of Death is standing right between them and it, saber in hand and active.
 * Call of Duty 4 has two of these. "All Ghillied Up" is a stealth-based Sniping Mission, and "Death From Above" puts you in the gunner's seat of an AC-130 gunship.
 * There's much to be said, after being in missions where you're outgunned and outnumbered, to be in a mission where it's the enemy and their AKs versus you and your 105mm howitzer, 40mm rapid-fire cannon, and electric minigun. Boo-yah!
 * "All Ghillied Up" is a particularly masterful example of a well-done Unexpected Gameplay Change; the first hint that it's going to be mostly stealthy is when as the game fades into view of an empty field of grass, your companion is only revealed when a piece of the scenery gets up and creeps forward.
 * World At War has its own Gameplay Change in the form of "Black Cats", in which the focus shifts from taking on the Japanese/Germans on the ground to shooting down Zeroes over the Pacific from the gun turrets of a Catalina flying boat.
 * This trope has been used since the beginning of the series. The first game has two levels where you drive a T-34 tank through a fortified German city. The second game followed suit, putting you in a Crusader tank fighting enemy armor in the Libyan desert, and World at War had one such mission as well.
 * The expansion pack, United Offensive, has a level where you play as the gunner of a B-17 bomber, defending your plane from a ludicrously large number of German fighters.
 * At the end of Crysis, which has been almost entirely on-foot first-person shooter action with minor, optional car usage, an entire level takes place with the player driving a VTOL fighter craft, which handles like a pregnant cow, and which you have to engage in dogfights with.
 * You were given a prep course for that when you had to drive an alleged tank which has lousy traction, can't push through a picket fence, has no weapons stabilization what-so-ever, and doesn't even let you use the binoculars you have while walking around.
 * In Geist, the final boss is an unexpected genre shift. Then again, it's been a Stealth, a Puzzle Game, and a First-Person Shooter, so turning into a Space Shooter probably wasn't too much of a stretch.
 * The Quantum of Solace video game had an unexpected setting change. Just after the player completes the sinkhole level, Bond has a flashback. Oh, huh, it's the opening scene of Casino Royale. Okay, it's a Character Development Flash Back-wait, where'd the cinematic letterboxing go? This was not really mentioned at all in the game promotions.
 * The main problem is that, since Casino Royale didn't get its own game adaptation, the Quantum of Solace one mashed the two together, so on your first time through you never really know which movie you're going to be playing out at any time.
 * Halo: The Maw, Outskirts, and Halo driving sequences, and the aerial battles on "Two Betrayals", "The Arbiter", "The Great Journey", "The Covenant", and "New Alexandria". Also, the Arbiter mission involves stealth to some degree.
 * You could actually get through some levels of the first Halo game with Stealth alone. This usually occurs before you figure out how to break sequence and skip entire levels.
 * Halo: Reach turns into a Free Space/Wing Commander-style space sim for the middle chapter of "Long Night of Solace".
 * Red Faction  up until that point you don't have to use your brain much.
 * Also, one level has a Descent style flight-combat sequence. This may be a holdover from the game originally being concieved as Descent 4.
 * There are two parts in the game where you have to sneak. Although you can actually skip one of them just by not taking a certain clothing item.
 * The King Tiger Tank level in Medal of Honor: Allied Assault.
 * Soldier of Fortune: Payback changes from a run-n-gun FPS to a Nintendo Hard tactical shooter in its final mission, due to the large unexpected increase in the damage dealt by enemies.
 * Return to Castle Wolfenstein involves a particularly annoying sequence early on in the game where the player is forced to sneak through an entire level, and if the player is seen, they usually get a game over almost instantly because an alarm is sounded (only in rare cases can the player get away with killing the enemy and not having another turn on the alarm.) The reason for the annoyance lies in the RTCW enemy sight and hearing range, which is absurdly large, and makes sense for an FPS game, but for stealth it turns the entire level into a Scrappy Level.
 * And there's a glitch that can render the level Unwinnable in some versions. If you shoot out the last alarm (with a non-silenced weapon, I think), the truck driver will be alerted, although unable to sound the alarm, and you'll be unable to exit.
 * It's still playable even if the alarm goes off however because you can still deactivate it and further it just alerts the enemies on the map to your presence thus increasing the difficulty to the level of other earlier ID titles.
 * The tank and walker levels in Quake IV, in addition to a few Rail Shooter segments.
 * Team Fortress 2: The Halloween update added an MMORPG-style raid boss in the form of the Headless Horseless Horsemann: ridiculously difficult to kill and gives an achievement and a rare drop to the person who lands the finishing blow.
 * Team Fortress 2 has many unofficial modes made by fans of the game. First, you might be in a Vs. Saxton Hale game, where it's your team against the super-manly CEO of Mann Co., and then FortWars, where your team builds walls out of junk and then plays "keep-away" with the intelligence, either protecting it or killing the other team, and then it's off to PropHunt, where one team has been transformed into various bits of scenery (a haystack, a barrel, a wooden cow, etc.) while the other team must find them. The hunted can't use any sort of weapon, but the hunters lose health every time they fire their weapons, to prevent spamming.
 * Half-Life 2 had driving, boating and crane sequences to break up the shooting, as well as a Survival Horror chapter with sparse ammunition.
 * Riding the Styracosaurus in Turok 2's second stage, and the infamous pterosaur flying levels in Evolution.

Flight Sims

 * Pilotwings is mostly a simple game about training excercises on various kinds of aircraft. But halfway through, and again at the end, it suddenly turns into an action game where you have to avoid antiaircraft fire in a helicopter to rescue your instructors.
 * And again in the final stage, except that you're saving a government agent. What make this especially jarring is that you don't get any retry chance if you're shot down; it goes immediately to the Game Over screen...the implication being that you died.

Hack And Slash

 * Drakengard's Final Boss, in the game's hard-to-reach fifth ending, is not fought in the same way that other major enemies have been, Hack and Slash for ground enemies and Flight Sim for aerial enemies. The game orients with the dragon flying a circle around the Final Boss as it emits white and black colored circles. The player has to emit a white circle back for a white circle and so on with black circles, turning the game into a simplified version of Simon. That said, the patterns emitted by the Final Boss are soul-crushingly difficult to replicate at times.
 * There's a similarly frustrating battle in the sequel: On the path to Ending B (and the final ending), the protagonist Nowe is forced to fight . Surrounding the structure are several colored crystals (?). The "boss" only has two abilities--it glows with a colored light, and a shockwave. However, touching the boss while it's glowing is an instant kill. The shockwave is also instant death. The only way to damage the boss is to use the downward strike, and then hide behind the crystal that matches the color the boss is glowing. And then you only have a split second to jump off (or summon Legna and fly off) before the boss starts glowing again. The timing of your attack and the boss's color pattern can be very hard to gauge, and if you die you have to start all over again until you win.
 * No More Heroes intersperses hack-and-slash mayhem with open sandbox city exploration, item collection, a Galaga-esque space shooter sequence, public services such as cleaning up the park or mowing lawns, hitting a baseball through a row of enemies, and avoiding obstacles on a highway chase.

Maze Game

 * Possibly one of the most extreme changes, the arcade game Baby Pac-Man included an actual physical pinball machine. Play alternated between the video game and the pinball game. (Of course, it is pretty difficult to call this an "unexpected" gameplay change, since the pinball game was right there under your face from the start.)

Miscellaneous Games

 * Although Action 52 is itself a wild mishmash of games and genres, a couple of its games do this. The third level of "Ninja Assault" is a frustrating log-jumping level in the midst of beat-'em-up levels, and "Bubblegum Rosie" has an even more frustrating driving stage in between the first and third platformer levels. Cheetahmen starts out as an isometric beat-em-up similar to the first level of Battletoads, but is a platformer for the rest of the game.
 * Interactive fiction game Heavy Rain goes from tense, heart-stopping stealth and action hybrids to... playing on a construction site as a small child completely new to the plotline.
 * Not so much Unexpected Gameplay Change and more like Unexpected Gameplay period but the last episode of Umineko no Naku Koro ni contains some puzzles you have to answer to get bonus scenes and a choice which decides which of the Alternate Endings you get, its not much, but even this minuscule bit of gameplay was very unexpected for a series that for 7 episodes was a straight visual novel with absolutely no interaction whatsoever.
 * Video Game/Sin and Punishment: Successor of the Skies is a pretty standard rail shooter, up until the last stage of the last boss of Chapter 6 where it suddenly shifts to a side on Street Fighter like fighting game.

MMORP Gs

 * Star Wars: The Old Republic, meanwhile, features Star Fox-style rail shooter space combat.
 * Those are actually closer to being a call-back to the old TIE fighter and X-wing games.
 * While the majority of quests in World of Warcraft consists out of killing stuff, there are some quests that mix things up, such as flying on a fixed path to drop bombs or a few minigames connected to the various ingame holidays like juggling a torch.
 * Wrath of The Lich King added a new vehicle mechanic and a lot of opportunities to use it. Most of them include you mounting on something that amounts to a giant death machine and laying waste to hordes of enemies. These are undoubtfully awesome. Most of the rest have you take on something that's even stronger. These are fun if you like the change and are hated by the ones who find it hard, or by players who lack the coordination required.
 * A game that changes from 2d movement into 3d, at a boss fight that depends on precise positioning with no way to tell how far away, up or down you were, but retaining the poor camera controls. The Oculus is so bad they had to add a bribe (A new mount) to it to get people to stop abandoning groups as soon as it came up. This was intended as practice for an even worse raid dungeon with the same mechanic. The bugs that still run rampant, almost a year after release, such as things aggroing to you from far outside their normal range, that can only be fought on dragonback, but since you're in combat you can't mount to fight it, don't help either.
 * When people enter the Upper Spire of Icecrown Citadels they are confronted with a hallway where jets of cold burst from the walls, transforming the game briefly into a timing based obstacle course. Despite being so incredibly easy than any platformer would burst out laughing on being told they presented a challenge, these have been known to kill the same person multiple times, as they die, get brought back to life, then run right back into the icy jets. Part of this stems from the first of said jets being five feet in front of where you zone in, so those continuing to hold forward through the brief loading screen out of habit are quick to be instagibbed. These kinds of challenges are located in several dungeons and raids and are collectively known as "Frogger".
 * The more well-known version of Frogger is found in Naxxramas. After killing Patchwerk in the Abomination Quarter, to proceed through the raid, you need to avoid several rows of green slimes that move in one direction; very similar to the game "Frogger". This was known for killing more raid members than the actual boss fight preceding it. Similarly, several elevators (most notably, the one in Serpentshrine Caverns) are known as "the elevator boss", since apparently waiting for a very very tall elevator is too difficult a concept for the average WoW player, causing many players to jump early and fall to their deaths.
 * Heroic Deadmines in Cataclysm takes this up to eleven, under the effect of the true final boss' mind-altering nightmare poison, you hallucinate various nightmares involving the other four bosses, challenge one and three include, in order, running down a narrow ramp (the sides are flooded with fire) while avoiding icicles that fall from the ceiling and will one-shot you, the third challenge can best be described as a Super Mario Brothers reference involving fire bars, but electricity instead of fire.
 * Peacebloom vs. Ghouls is essentially a tower defense game disguised as a quest chain, using a garden full of magical plants to defend a farm against marauding undead. Sound familiar? It should. The minigame is a deliberate tribute to PvZ with the ultimate prize being a vanity pet modeled after one of the flowers from the source.
 * In Final Fantasy XI, Parradamo Tor is a giant monument to this trope. If you want to complete the Chains of Promathia mission series or have a fight in Boneyard Gully, you're forced to climb it, an activity that more than anything resembles a cross between maze-crawling and tightrope-walking.
 * City of Heroes is mostly a classic MMORPG, but one phase during the Behavioral Adjustment Facility trial bears more than a passing resemblance to a Tower Defense game.

Platform Game

 * Modern platforming games such as Sly Cooper and Ratchet and Clank often have you enter races in order to gain items or otherwise progress in the game.
 * The Sly Cooper games have also thrown in vehicular combat, Robotron 2084-esque shooting segments, and rhythm-based sequences as well. Some fans of the stealth-focused first game have complained that this wrecks the point of the series.
 * Most will agree the rhythm battle with Mz. Ruby is among the best boss battles in the series.
 * The Tomb Raider series has various driving sequences, ranging in quality from fun to Scrappy Level territory.
 * The dreaded Underwater Propulsion Vehicle sequences on the Down the Drain level Lud's Gate.
 * Tomb Raider IV: The Last Revelation opens with a sixteen years-old, defenseless Lara. It's a tutorial segment, so no big deal... until Tomb Raider: Chronicles, where a lengthy segment with Young Lara is tossed in the middle of the game. Not an unwelcome variation for a game that had become so formulaic by then, but still unexpected and potentially troubling.
 * The motorcycle stages in Legend, one of which is an obvious Homage to Indiana Jones and the Last Crusade.
 * The Jak and Daxter series is rife with these, containing everything from races to skateboarding to stealth to rail-based shooters, and etc...
 * The games themselves go from the bright and happy, fantasy-based Jak and Daxter, to the darker, more sci-fi with GTA mixed-in feel of Jak II. And the most Scrappy Level of all in this series is easily a very early mission in Jak II involving be chased by a tank from its perspective. The difficulty spikes hideously there.
 * The Scrappy Level is definitely the rail-based shooter level where you have to destroy the tanker, particularly on Hero Mode, where the number of guards and their increased resistance to damage makes it near impossible. That level makes every other, including the final boss, look easy.
 * The really frustrating part is that after sitting still and taking out forty guards spewing out of every orifice of the level, fighting the tanker is actually easier.
 * Kid Icarus, a classic NES platform game, unexpectedly becomes a side-scrolling shoot-'em-up in the last level.
 * Which Uprising would end up adopting as the standard gameplay type. Even then, the game had a few examples of this trope such as:
 * Chapter 18, which becomes a Kingdom Hearts style melee-focused Beat'Em Up due to  It also flips the usual Air Battle - > Ground Battle formula.
 * Chapter 19, which throws an unexpected High Speed Battle at you for the boss fight, which annoyingly doesn't really explain the controls to you until it's probably too late.
 * The air portion of Chapter 20, which has you  uses the same shooting mechanics as normal, but plays like a top-down Bullet Hell game.
 * And Chapter 22, while previous stages have been roughly 50% Air, 50% Ground Battle, this stage is all Air until the boss.
 * Bucky O Hare and The Toad Wars, a very good but rather obscure NES platformer, also becomes a (very good) side-scrolling shoot-'em-up in the last level.
 * Metroid: Zero Mission features a Stealth Based Mission in which Samus loses the standard power suit and must navigate through an enemy-infested fortress armed only with a weak, slow-charging stun pistol.
 * Super Mario Galaxy loves to shift from 3D gameplay to 2D gameplay, but the opening level of Super Mario Galaxy 2 takes the cake -- it starts on a strict 2D plane, then becomes 2.5-D (as in that Mario can roam freely around the ground, yet the game is still in a sidescrolling state), and finally fully 3D by the time Mario reaches the castle.
 * Super Mario Land, while mostly a standard Mario game, includes a few side-scrolling shooter levels, including the final level and boss.
 * Star Fox Adventures has it a bit backwards--while the Star Fox series is a shooter, Adventures was a Zelda-esque game, so when the game threw in "classic-style" shooting elements, it felt a bit weird. One can attribute this to it's origins as Dinosaur Planet, a game that had nothing to do with Star Fox.
 * Played straight with the Aquas submarine level in Star Fox 64, and the two tank levels.
 * The difference is in the absent crosshair. It appears briefly when one does a Charged shot, but because all charged shots are auto targeting the enemies, it only purpose is to show which enemy is going down when you release the A Button. In other words, aiming is more difficult.
 * Sonic Adventure added a number of different genres (one for each character) to the Sonic series that had been fast paced platformers. For example, Big has a fishing style, with Knuckles you have to find Emeralds shards, Tails has races, with Amy you have to run away from a 'Gamma, and with E-102 Gamma you have to shoot things. There's a few shoot 'em up stages too.
 * Sonic Unleashed introduces a werewolf-like transformation for Sonic, which is slower then Sonic and consists of a lot of bashing.
 * The day stages were this as well. Up to this point, the games had all used the Adventure formula, which began as somewhat the Classics in 3d, from a certain point of view: Running and jumping, attacking enemies and landing on platforms, the only major changes being the homing attack, being faster paced, more story driven and less emphasis on rolling, Sonic's original gimmick. When Unleashed came around, this all changed and it became more speed orientated, and since Unleashed fans have officially declared the return of Sonic the Hedgehog.
 * And then there were the Tornado Defense and Gaia Colossus stages.
 * Sonic 3D Flickies Island involves killing badniks and freeing flickies...until Panic Puppet Zone. In Act 1, they are in pods instead. In Act 2, there aren't any flickies at all as the goal is to get to the top of the level
 * I Wanna Be the Guy does this twice in the Hall of Former The Guys. In Sinistar's room, opening the way forward requires playing a game of Break-Out, and in the room after it, you mount the Vic Viper for a brief shooting segment.
 * In Kirby Super Star, Milky Way Wishes interjects the usual Kirby gameplay with a shmup section. Most Kirby games end with an Unexpected Gameplay Change.
 * Additionally, The Great Cave Offensive tries to tinker the series' linear-platforming gameplay into something more like a Metroidvania, but it doesn't quite make it. There's also the RPG boss, but that's really more of a joke.
 * Kirby & The Amazing Mirror was a successful Kirby one.
 * Super Star Wars: Return of the Jedi ends with a really irritating, escape sequence involving dodging obstructions. It quickly become ridiculously fast, turning into an almost Battletoads level sequence.
 * The Death Star trench run in the first SSW game was also a big ugly unexpected gameplay change.
 * Not counting the three other 3D vehicle shooting levels.
 * Similar to the Star Fox example, many people complained that the Donkey Konga games were taking the Donkey Kong series away from platforming, even though they were clearly spinoffs, not sequels to the main series. One hopes Donkey Kong Country Returns will shut the complainers up.
 * Speaking of Donkey Kong, Donkey Kong: King of Swing had a level in the last world that had no pegs at all, consists of only one area, and revolves flying around a rocket barrel. Not to mention that the final battle against King K. Rool.
 * Donkey Kong 64 had two different arcade machines: one for the original Donkey Kong and one for Rare's Jetpac. They seemed at first to be amusing distractions...until you get to the final door in the final level and find that it's embedded with Nintendo and Rare icons; you have to beat the original Donkey Kong and score enough points in Jetpac just to reach the final boss. For many uncoordinated children who hadn't grown up with those games, this was a bit of a brick wall.
 * Donkey Kong Country 3: Dixie Kong's Double Trouble has a level, Krack-Shot Kroc, where an offscreen villain is continuously trying to shoot you, with a big crosshair showing where his next shot will go. An Unexpected Gameplay Change comes in one of the bonus areas of this level, where you control the offscreen cannon and must kill all enemies in the bonus area.
 * The boss of the same world is a snowball fight that borrows its mechanics from a minigame two levels world before.
 * The Rocket Knight Adventures series frequently breaks up the platforming with shmup segments, and on top of that each game has one boss take the form of an extremely simple Fighting Game.
 * Spyro 3: Year of the Dragon included a lot of interesting gameplay changes as optional side missions, including a two-part FPS sequence where you take control of an ape with a laser gun. As a fun homage, the two parts of this sequence were titled "You're Doomed!" and "You're still Doomed!"
 * The mid to late Spyro games (Spyro 2 and the Gamecube games) are guilty of this too. In Enter the Dragonfly there are minigames where Spyro gets to pilot fighter planes and tanks.
 * N64 Platform Game Rocket: Robot on Wheels featured several "vehicles," which could be ridden around the worlds; this itself didn't necessarily institute a gameplay change, but it frequently led to "racing" segments (or Pass Through the Rings). Also, one section of the game includes a miniature roller coaster-building sim. It's not quite a mini-game, but it's still... unusual.
 * Banjo-Kazooie saw the first phase of the final boss defeated with a TV-style quiz show.
 * Banjo-Tooie featured several "Breegull Blaster" segments, where the game's usual platforming action strayed and the game became a first-person shooter with Kazooie as the gun. Not only did you fight a boss this way, but all of the maps from these modes were included in the multiplayer mode as "shootouts." Both the maps and the control scheme replicated those from Rare's FPS Goldeneye.
 * Rare struck it backwards again with Banjo-Kazooie: Nuts & Bolts, which strayed from the series' typical platforming to be a user-generated vehicle game with some platforming in the Hub Level.
 * The PSP game Hammerin' Hero is a side-scrolling 2.5D platformer for the first eleven stages, and then the last level turns into a free-scrolling R-Type clone. Hell, even the Big Bad (who you fight in the second-to-last stage) fights you in a spaceship which looks a helluva lot like the R-9 Arrowhead, complete with Force Bit.
 * Mischief Makers, a side-scrolling platformer, has one level which consists of a series of Olympic-style events, with gameplay not unlike that of Track and Field for the NES. Furthermore, one of the events in this series is an Unexpected Gameplay Change in itself: amidst a bunch of athletic events is a math competition.
 * Another event in that stage that stands out (Though not to that extent) is the one where you have to catch balls in a pot while making sure none belonging to the other team gets in. (Which makes you wonder how you carrying the pot is fair to the other team
 * And getting the gold gem in said level without a turbo controller is nigh impossible.
 * Just remembering that minigame is enough to cause thumbaches.
 * It makes up for these events by putting the single greatest boss fight ever at the end of them.
 * You mean the one where you play dodge ball with a cat? It Makes Sense in Context.
 * More like the part where you, a robot girl who grabs, shakes, and throws things, is riding a cat chasing after an anthropomorphic wolf on a transforming motorcycle, catching and throwing back the missiles he fires at you. You can also hop onto a missile, making you a robot girl riding a cat riding a missile!
 * The final eight stages of Plok are a gauntlet run of Unexpected Gameplay Changes (arguably making the game's homestretch Those Eight Levels). Each stage of the Fleapit puts Plok behind the wheel of a different vehicle with touchy controls and (in most cases) nigh-useless weapons. The final stage arms Plok with the "Secret Super-Vehicle", a weapon so supposedly awesome that the manual only shows it in silhouette.
 * The Asteroid Belt and Final Boss stages in Adventures of Rad Gravity, where you're in zero gravity and have to use your gun to propel yourself.
 * The console versions of Toy Story were for the most part pretty standard 2D Platformers....except for that one level which was played from a DOOM style first person perspective.
 * The unlicensed Mega Man X ripoff Rocman X/Thunder Blaster Man has an Auto Scrolling motorcycle shmup level late in the game.
 * Magic Planet Snack has four microgames:
 * 1. Normal game. Take the orbs, but don't eat trolls or lava.
 * 2. Hyper mode. Achieved by picking up 10 orbs. All things except trolls turn to cake. Each cake is worth 1000 points, twice as much as an orb.
 * 3. Wizards. In the center of each planet is a wizard with two familars and 1-5 TVs. Take all the TVs and you can then attack the wizard directly. The two familiars are shooting bullets during this time, and the familiars can only be eaten in hyper mode.
 * 4. Satellites. In between planets, satellites will appear and lay mines to block your path.
 * In Dynamite Headdy the normal (though not very normal) platforming is replaced with a flying shoot'em up for one level.
 * Prince of Persia: The Two Thrones has two chariot races. Two thoroughly infuriating chariot races. Otherwise, the game was an excellent balance of platforming and combat.
 * Occurs frequently in the Mega Man series, such as the Rush Jet shmup sequences, the Auto Scrolling Level in Dr. Cossack's Castle, the waverider level in Mega Man 5, and the snowboarding sequences ("Jump! Jump! Slide! Slide!") in Mega Man 8.
 * Particularly memorable in the Game Boy Mega Man V, where you begin by dodging indestructible asteroids, then taking on Mooks with the Breath Weapon Rush is now equipped with, then dodging lasers on the way to fight the Wily Star.
 * The Lion King was a side-view platformer except in the wildebeest stampede level, which had Simba racing towards the camera.

Puzzle Game

 * Parodied in Portal when GLaDOS "accidentally" sends you to a battle-droid training chamber because the usual testing area is being repaired. (Given that, this is almost certainly a half-truth at best.) Instead of figuring out how to get around strange logic puzzles, you need to use your skills to deactivate the security drones.
 * Soon after this point the whole game begins to subtly genre shift from a simple, plot-less puzzle platformer to a more straight-up platformer with puzzle elements added in, with a storyline resembling survival horror more than anything else.
 * Note that the 'straight-up platformer with puzzle elements added in' is, essentially, just making the story part of the puzzles.

Real Time Strategy

 * Starcraft: Ghost was supposed to feature, near the end of the game, you going around in a tank and blowing the crap out of everyone, after an entire game of sneaking around.
 * See this Penny Arcade strip.
 * The Orc campaign in Warcraft 3: The Frozen Throne suddenly turns out to be a full-on RPG, rather than the strategy + slight RPG mix of the previous seven campaigns.
 * Though the Orc campaign isn't part of the main story (as it's unlocked from the start) so it's not very sudden.
 * What's more sudden is the bonus tower defense level in the alliance campaign.
 * And directly after the tower defense level is a Defense of the Ancients-style level!
 * Pretty much every Tiberian/Red Alert Command and Conquer game has at least one campaign mission that is more real-time tactical than real-time strategy. The player will control a small (1-4) number of elite commando units and have to use a combination of tactics, stealth, and scripted events to outmaneuver a militarily superior foe. The original Red Alert was particularly fond of these, often setting them inside missile silos or bombed-out towns in central Europe.

Rhythm Game

 * The boss songs in Guitar Hero 3, where you essentially were buffeted by random status effects and had to use your own random status effects to try and make the other guy fail.
 * Despite all the flack Guitar Battle has gotten, it was actually a pretty cool concept, and more in tune with the "beat the best to be the best" theme of the game than simply playing songs. The problem was that you HAD to win. You literally would not get another song or venue, ever, until you won the battle. Thankfully, Neversoft realized that this was a lousy idea and put only a couple of token duels in World Tour before eliminating them as a requirement for good.
 * This in spite of the fact that changes to the format in World Tour made the guitar duels no longer gameplay changes. Guitar duels worked much more like they would in reality- guitarists trading licks over a consistent rhythm, played out like any other song, rather than forcing the player to use power-ups to upset the other guitarist. This also removed the issue of an up-and-coming wiping the floor with veteran shredders at ratty gigs.

Role Playing Game

 * In Mass Effect 2 when you suddenly have to play as Joker, (your pilot with brittle bones disease who can't fight) where you have to avoid/flee enemies that you would normally squash like a bug, it has a very survival/horror feel to it, especially if you make the wrong move.
 * In possibly the earliest example of the trope, the first installment of Ultima, a turn-based high fantasy RPG, required the player to buy a spaceship, engage in real-time one-on-one space combat, and become a "Space Ace" in order to finish the game. And you thought that astronaut on the cover was just bad art...
 * Final Fantasy VII contained vehicular combat, snowboarding segments, chocobo-racing and a real-time strategy minigame (the last of which could admittedly be bypassed simply by running straight away to the boss). It even had an ongoing Dating Sim pastiche! There's a reason it's the Trope Namer for Sidetracked by the Gold Saucer!
 * VII also has the game where you have to give Priscilla CPR. This strangely never comes up again, making it both a Unexpected Gameplay Change and Big Lipped Alligator Moment.
 * Final Fantasy VI had the opera scene. One had to remember a couple melodramatic (but hey, it's opera after all) lines from an opera; any mistake would end the scene and require it to be restarted. Then again, this is considered one of the best scenes in the game.
 * Final Fantasy VIII and IX both contain card games. It can be completely ignored in VIII if you choose, but it is a good way to get many rare items and spells. There is one short portion of IX that requires you to play, but you only have to win a few battles. However, you miss out on a nifty item if you don't win all the card battles. Besides that, the only reason to play the game in IX is to... get all the cards.
 * VIII also features a... fistfight between the main character and a mook with a jetpack. Fortunately, if you failed you were allowed to restart at the start of the sequence and choose to tone down the enemy's health.
 * IX also features Chocobo Hot and Cold where you use a chocobo to dig around in a forest (and a few other areas) to get items. You also find treasure maps that guide you to treasures spread around the world that you can dig up with your chocobo. This is entirely optional, but you get some of the best weapons and armor in the game from it, sometimes much sooner than you should.
 * Final Fantasy games from V to IX all feature sections where you have to race through an area with a timer.
 * The Pokemon Contests in Pokémon Ruby and Sapphire.
 * They've been carried over and made even more complicated in Pokemon Diamond and Pearl. If you want to master them, you may have to actually train Pokemon specifically for contests, giving them different moves than battle-concentrated Pokemon, and manipulating their natures to fit the contest you want.
 * Specific natures aren't exactly needed. I managed to get the Smart ribbon Master in DP using a Milotic that had no points in Smart to speak of. Ended up easier than Beauty, ironically enough. Of course, you still need a scarf, need to know what items give what boosts in what theme, know how to dance just right, know which opponents screw each other up or benefit each other... In other words, Guide Dang It!
 * Diamond & Pearl also have two new mini-games thrown in to take advantage of the DS's touch-screen and wifi capabilities: (There are benefits to playing them at the same time as friends.)
 * A "Poffin-making" game consisting of making circles with the stylus, adjusting the speed and direction in reaction to signals on the screen. The main purpose of this is to make your 'mons perform better in one phase of the contests.
 * An "underground" game allowing you to encounter other players, and set harmless "traps" for them. There's also a mini-game within the mini-game that's somewhat similar to Battleship. Both of these parts are encouraged, to achieve 100% completion.
 * HGSS has the Pokéathelon, which is basically the Olympics with Pokémon!
 * In Pokémon Ranger: Guardian Signs, there are levels where you have to chase someone underwater by diving down and levels where you have to dodge swarms of energy bullets.
 * The Gummi Ship mini-games in Kingdom Hearts, where you go from an Adventure Game to piloting a Star Fox-esque spaceship against waves of enemies. In Kingdom Hearts II, the Atlantica world throws you into a sort of Rhythm Game; this was possibly in response to the original Atlantica, which stayed in-genre but added a badly-implemented third dimension. Finally, one of your Summons allows you to temporarily switch to "FPS Mode".
 * Kingdom Hearts Re: coded is, for the most part, an RPG with a battle system closest to Birth by Sleep, but every level ends with something different. Olympus, for instance, turns into a turn-based RPG (appropriate, since Cloud is there).
 * Birth By Sleep. Disney Town. Basically, you have three minigames, in each character's story you have to do one of them. They are: Kart Racing, a Rhythm game and this volleyball...thing. And you HAVE to do the one in your storyline.
 * The (optional) Galaga-esque flight segments of Jade Empire.
 * Blitzball in Final Fantasy X.
 * Super Mario RPG has many minigames, which themselves have UGCs; one minigame has you sliding down a waterfall in one part and riding barrels down a river in the next, and another has you riding in a mine cart, alternating between Mode 7 sequences and Minecart Madness.
 * Paper Mario: The Thousand-Year Door featured small sidequests in between chapters where the viewpoint shifted temporarily to Peach or Bowser. Three of these mini-chapters starred Bowser playing through parodies of levels from the original Super Mario Bros..
 * Super Paper Mario has one Boss Battle that becomes a pastiche of Dragon Quest, and another had a Dating Sim-esque segment before the actual fight. There's also an Unexpected Shmup Level.
 * How about Super Paper Mario itself? Considering it's a platformer in a series that originated as an RPG, sure there are some RPG elements in it but you still can't deny it feels nothing like the previous two entries in the series.
 * Star Wars: Knights of the Old Republic contained mandatory (though pathetically easy) arcade sequences where the player had to take down Sith fighters with a ball turret, as well as Random Encounters with Sith fighters when flying between planets. A more annoying mandatory sequence involving swoop bikes was preceded by a long, unskippable cutscene, forcing the player to repeat it over and over in case of defeat during the race. The sequel contains no random encounters, and the plot-driven arcade sequences are no longer mandatory.
 * Rather bizarrely, the sequel had a brief sequence with you manning one of the Ebon Hawk's guns against a horde of Sith troopers. Even more strangely, while there was no reward for killing them with the turret, letting them board the ship and then beating them hand-to-hand was worth a healthy chunk of XP.
 * The NPCs in Breath of Fire 4 force Ryu to perform so many mini-game based quests, that players may feel justified in joining Fou-Lu to blow them all up in the Bad Ending.
 * The Dynasty stage in Mega Man X 8, where you go from 2D running and shooting to a 3D hovercar chase reminiscent of Attack of the Clones.
 * Nearly every X game has at least one auto scrolling hoverbike level since X4. X8 has two of them.
 * Quite painful in Xenogears when you enter into a gear combat tournament. This brings in a rather simplistic Street Fighter style combat system, despite the fact that you're not actually doing anything different than when you are usually fighting in your gears (which is standard RPG style).
 * Baten Kaitos: Origins has a brief stealth segment, as well as a couple of scenes where you have to collect evidence to solve a bombing.
 * And its predecessor, Baten Kaitos: Eternal Wings and the Lost Ocean has a Block Puzzle. A really diabolical Block Puzzle, thanks to the perspective not quite lining up with the basic directions, meaning half the time you'll be straining up against the block and it won't be moving. There's also the Trail of Souls, an Unexpected Shmup Level made to troll those who are going for Hundred-Percent Completion, and the Ice Goddess and Wizard Shadow battles, both of which seem to think that regular fights in Eternal Wings aren't quite luck-based enough.
 * Steambot Chronicles, a.k.a. "You got some bemani in my Humongous Mecha Wide Open Sandbox!".
 * The World Ends With You has Tin Pin/Marble Slash, which is a kind of mini game where you have to knock other people's pins off a platform using your own pin. Thankfully, you only have to play it once, against a very easy opponent, and can stack the odds in your favor six pins to two.
 * And then this trope gets pushed much further in the Omake bonus game Another Day, which is all about Tin Pin Slammer and has a complete shift in tone with hilarious results. It's like Square-Enix wrote their own crack fan fic.
 * Hellgate:London, a horror-themed FPS/RPG, has one mission in which you control a group of fighters which turns the game into a (really bad) RTS. This section is also incredibly much harder than the rest and is generally beaten by triggering a bug to avoid losing, then chain airstriking the boss for 20 minutes.
 * And don't forget the turret section.
 * The RTS mission "The Wall," is an unanimously Scrappy Level. Your Mileage May Vary on the ground-to-air firefight "Gundown"; some players enjoy it, and for some builds it's too easy to be annoying.
 * Marvel Ultimate Alliance makes you play some Pitfall with the character who activated the machine as the game character. This can be pretty annoying when characters that can usually fly or teleport keep falling into pits.
 * And also an instance of Breakout where one of your characters actually pushes the paddle left and right and plays the game, while the others should try to avoid getting hit by the ball.
 * Space Rangers 2 starts off by being a RPG-esque space arcade/sim with economic elements. Then there's the RTS sections with Humongous Mecha, which you also can control directly in third person view. Then there's the text-based missions which range from logic puzzles, to math excercises, to "choose your own adventure" style sequences. And then there's the straightforward arcade "fly around and shoot everything" sequences inside wormholes.
 * Sometimes these text-based missions turned out to be economic simulators. Once it even became a text version of the Space Rangers itself. And it's hard to tell what exactly it will turn out to be when you take the quest. Just what are developers expecting from players?
 * Final Fantasy IX had a number of minigames, including a footrace, a frog-catching game, a treasure hunting game, and a game where the player has to make a frog sneak up to steal a key without being noticed by a monster. Fortunately, most of these games are entirely optional, merely giving the player additional treasures and bonuses that make the player characters stronger but otherwise aren't needed to beat the game.
 * Final Fantasy X 2 has a lot of these. There's enough focus on combat to keep it from being a complete Gameplay Roulette, though.
 * Two of these game sequences, a shooter and a bizarre game involving coins and math, were required to continue the game. The later in particular was annoying, because you either had to be very good at it, or had rare coins in your possession, to beat it. Since the tourney in Chapter 3 forces you to use four specific coins, you had to have some skill in getting multiples to get some of the quotas (especially Shinra's 50 quota grid).
 * One only has to play these games, not win them -- thankfully this holds true for most of the (many) minigames in X2. Winning netted you extra goodies that could make the rest of the game easier, but it wasn't required to continue.
 * Unfortunately, doing well at Sphere Break is REQUIRED for One Hundred Percent Completion, as this minigame is where you get the Lady Luck dressphere and a couple of garment grids.
 * Mario & Luigi: Bowser's Inside Story has several plot-specific mini-games, ranging from a top-down shooter to a rhythm game.
 * Baldurs Gate II is a straightforward party-oriented Western RPG based on the Dungeons & Dragons ruleset -- except for one part of the Watcher's Keep area that's a text-based dungeon crawl.
 * Threads of Fate (aka Dew Prism) requires you to play three platform jumping games before you can talk to Fancy Mel and continue your quest.
 * Chrono Trigger features a jet bike race in a post-apocalyptic future.
 * There was also the portion where your weapons were confiscated and you had to use stealth to avoid enemies. Having Ayla in your party makes things a bit better, though.
 * At one point in Shadow Hearts: Covenant, most of the team is captured by the villains -- the only one that escapes? Blanca, your Big Badass Wolf. This triggers a Stealth Based Mission.
 * Specifically, it is a direct parody of Metal Gear Solid: In order to hide behind walls, the wolf gets up on its hind legs and peers around the corner.
 * Nie R is kind of the king of this, it's an action RPG with sudden gameplay changes to 2d sidescrollers, text based adventures, and heap helpings of bullet hell.
 * Fallout: New Vegas is a pretty straightforward FPS/RPG. Then the Dead Money DLC turns it into a pretty straightforward Survival Horror.
 * Anachronox is a JRPG-style game with unskippable debris-dodging, rail-shooting, and turret-defense sequences. Also included are different minigames for character skills, from coin-flipping to democratic debate.
 * Instead of a traditional sword battle, one of the duels against the Quirky Miniboss Squad in Brave Fencer Musashi required the player to play a version of Simon, with rhythm elements incorporated.

Shoot Em Up

 * If a Touhou game, a Shoot'Em Up series, has any decimals in its numerical listing, it's one of these. 7.5 and 10.5 are both fighting games, while 9.5 is... think Pokémon Snap, except now the Pokémon are trying to kill you. Sometimes with lasers.
 * A bizarre twist on the concept is used in one of Yukari Yakumo's spellcards, where she uses her Reality Warper superpower to "change the game you are playing", and make you supposedly suffer attacks from every shooting game at once. Of course, in-game it's hard to tell the difference if dozens of lasers and hundreds of bullets are coming from space ships or monsters.
 * The PC-98 Touhou games had gameplay changes between games from the first one, where you hit a ball around, to the second one, which was the first Shoot'Em Up, to the third, which was a multiplayer shooter, and then the last two which went back to Shoot'Em Up
 * During the final mission in Metal Slug 3, the player characters board "Astro Slugs", and the game turns into a top-side scrolling shooter.
 * The final stage of shoot-em-up Dogyuun involves you boxing two robots to death with a giant robot of your own...and there is no foreshadowing to this whatsoever unless you play the two player mode. Watch it here!

Simulation Game

 * In Princess Maker 2, a Raising Sim, if you get your daughter a job as an Adventurer, you play through RPG-esque sequences in four different lands; indeed, half the content of the game is in this part.
 * Mild example: in both Descent: Free Space and Freespace 2, an ambush early in the game led by some enemy flagship inevitably results in you being part of the mission to take it down - in a bomber. Command comes up with some excuse as to resources being stretched to justify assigning a fighter squadron to bombing work, and your squadron leader gives you a quickie on bombing on the briefing screen. While not at all a big deal to players who've done the campaign at least once (you get assigned to bomber squads later on), it's incredibly disconcerting to new players for not only do bombers handle much differently to fighters, bombing capital ships is radically different to dogfighting. There's no bombing tutorial for both games either, in a series that otherwise has great tutorials for everything else (even escorting ships from bombers has its own tutorial).
 * The last in the series of Star Wars: Rogue Squadron games on the Game Cube did this when it introduced on-foot sections and/or levels to what had been a spacefighter combat game.
 * This is because the RS series is descended from Shadows of the Empire. SotE was mostly a 3rd/1st-person shooter on foot, but also featured a number of Unexpected Gameplay Change sequences. While the game as a whole was decent but unremarkable, one of the aforementioned sequences (The Battle of Hoth from Episode V) got enormous praise, so the developers decided to make an entire series out of it.
 * How do you raise your Mons' stats and earn money in Monster Rancher EVO? Not by entering them in tournaments, as you would in previous Monster Rancher games. And not by putting them through a series of training regimens. Instead, you take them to the circus and suddenly find yourself playing a DDR-style or "Simon Says" matching-style rhythm game. With an accordion. Really. Woe betide you if years of simple sim games have weakened your reflexes, because you're never going to get ahead in the games if you don't win them.
 * Freelancer has one mission you need to go into race course. It can be hard doing that mission using freighters.
 * In the final level of Hunt for Red October, it changes from a submarine Shoot'Em Up to an action platformer where you have to disarm bombs on the sub.
 * X-Wing Alliance does this. Most of the game it's a fun dog fighter/space superiority game. Then suddenly the final mission is an obstacle course.
 * Although you could it coming from a mile off. Whole game building up to you piloting the Millennium Falcon at the Battle of Endor. Hmm, wonder what will happen now. That said, X Wing did this too.
 * X3: Reunion has one in the second mission, where the space simulator combat of the rest of the game is replaced by an incredibly buggy, poorly implemented rail shooter sequence.
 * Not to mention the very annoying banter between your pilot and the pirates.
 * The Tokimeki Memorial series of games often feature RPG elements thrown in for some reason. If you go on a date with a girl there's a possibility of being attacked by thugs. Losing gives you a very bad reputation with your date. Winning ends the date but gives you a relationship bonus. Also during the school trip you'll be attacked by a mongoose, deer, or aliens but you're given a choice, run away alone (very very bad relationship hit), run away together (bad relationship hit) or fighting. Losing here will still give you a bonus to your relationship (because at least you tried) but winning will of course make the relationship much better. They can be especially tough fights if you've got no sports stats or after school club.
 * The second Tokimemo game makes it even worse if you end up having the same girlfriend as one of your two male friends making it IMPOSSIBLE TO WIN if you fail to beat them. Bonus points with Akane who you have to beat up her brother several times in order to win with her.
 * Anghel's route in Hatoful Boyfriend turns into an RPG battle when he rushes in to save you from Doctor Shuu.

Sports Game

 * The darts minigame in Backyard Baseball 2005. One could also consider the Kooky Kraken in Backyard Skateboarding, where you do not control your skateboard at all.
 * One of the events in ESPN International Track & Field is Rhythmic Gymnastics, which plays just like Dance Dance Revolution.

Stealth Based Game

 * The largely slow-paced Metal Gear Solid series usually features at least one hectic, run-and-gun segment per game. Metal Gear Solid 2 features a relatively long underwater swimming sequence.
 * And Metal Gear Solid 4 features a major fight scene between Snake and Ocelot. Nothing unusual about that, except  Of course that doesn't really matter since it's completely  awesome. 
 * Another boss battle does something similar in which
 * Snake's Revenge featured Rush'n Attack-esque side-scrolling segments in which the only way Snake can conceal his presence whenever the enemy faces his direction is by crawling on the ground. Oddly enough, setting plastic explosives to kill enemies does not trigger the alarm like it does in the regular areas.
 * Relatedly, in Metal Gear Solid 3, if the player saves their game and turns it off right after Naked Snake is captured in a cell, the next time they turn it on they will be subject to an Easter Egg which isn't just a genre shift, it's a complete game shift.
 * And then there's the fun of the completely non-canon skateboarding minigame in the PS2 version of Metal Gear Solid 2: Substance - one of the most unexpected, stupid and yet somehow incredibly enjoyable worksafe minigames ever conceived.
 * The sword gameplay in Metal Gear Solid 2 Sons of Liberty. Unlike all the weapons you have been using in the game, you have to use the Right Analog stick to perform slashing combos.
 * The stealth recon levels in the Rainbow Six series. Tend to be Scrappy Levels.
 * In  ~Assassin's Creed: Brotherhood~ , part of the mission to destroy  is an Unexpected Shmup Level, while destroying   culminates in a flight-action sequence.
 * Also, Sequence 8 has all of the player's weapons disabled and you're only able to use
 * In Assassin's Creed Revelations Den Defenses are Tower Defense minigames, while the sections where you dive into Desmond's history after collecting Animus Data Fragments are first-person platformers that require the careful placement of geometric shapes to complete. All that's missing, especially during the final sequence, which, is a psychotic female AI snarking at you.

Survival Horror

 * In Resident Evil 4, the Del Lago (The Lake) boss battle occurs in a off-board motor boat in the middle of a lake, using harpoons. Additionally, for this installment's token escape sequence, you board a jet ski with Ashley and pilot your way through a relative direct but collapsing cave system (including jump ramps). Except for the levels where Ashley drives that slow truck, there are no other vehicular combat or vehicle-driving parts in the game.
 * In Code Veronica, the Nosferatu boss battle requires the use of a sniper rifle, which isn't used elsewhere, to hit its weak point.
 * Dead Space is somewhat notorious for its shifts from a survival horror to a Shoot'Em Up kind of mission on two occasions. The first time you are defending the ship from incoming asteroids and later you're fighting a boss. Both are regarded as being annoyingly difficult even ignoring the high standards set by the achievements.
 * The much-hated driving levels in Alone in The Dark 2008.

Third Person Shooter

 * About half way through the game Oddworld: Stranger's Wrath, the game switches from a bounty hunt where you go from town to town collecting outlaws to a survival game where you are the outlaw, the money you have been collecting is useless and everyone is out to kill you.
 * Enter the Matrix is largely a Third-Person Shooter but includes driving and hacking sections and concludes with a spaceship (well, hovercraft) combat sequence.
 * Giants: Citizen Kabuto did this four times. It changes from 3rd person shooter to tactical RTS to 3rd person magic-em-up to 3rd person rampage stomp-em-up. Seemingly at will.
 * To clarify, the game had 3 races, each with a different play style. Each race was firmly rooted in a single genre but the campaign cycled through the races to tell its story, leading to this trope. Multiplayer was an aversion due to the lack of race changing.
 * The rail shooter Sin and Punishment turns into a side-scroller in Stage 3-2, with disastrous results.
 * It Got Worse in the sequel, other than some air close rage combat that was well intergrated, at the end of one of the stages it turned into a fighting game, with horrible boundries that would make the Lord Of Tekken rage.
 * Jet Force Gemini is a gory, fast-paced 3D shoot 'm up - except for the one stage that's a kart racer. Complete with power-ups and a multiplayer option. Makes a bit more sense if you remember the game's engine was originally written for Diddy Kong Racing, but still...
 * Gears Of War 2 basically averts the trope. There is a chapter which has a stealth mission which was actually cut from the campaign, but can still be played. At the very beginning you are given the option of doing the stealth mission or going in guns blazing. So, it is not mandatory. In addition, if you do the stealth mission and are detected, the game just switches over to straight combat, just like if you took the guns blazing option in the beginning. So, all it does is give you the option of using a different style of gameplay, but it is not enforced, even if that is the method you try to use.

Turn Based Strategy

 * Subverted in Disgaea: A group of Prinnies, knowing they can't defeat Laharl in combat, challenge him to a baseball game, complete with diamond and Gratuitous English voice shouting "Play ball!" Laharl turns to Etna: "Kill 'em." Cue one of the most ridiculously fun fights in the game (throw a Prinny and it explodes, and all the enemies are Prinnies).
 * Disgaea 2 pulls the same trick during the Inevitable Tournament, with bowling this time. The battle is intentionally set up so that you can win the whole thing in one turn.
 * And the prinny that's set up to be the 'ball' is named '10-pounder'.

Wide Open Sandbox

 * Grand Theft Auto: San Andreas featured a couple of stealth segments in the main story, and even more in the form of sidequests.
 * Many of the missions were horribly designed, nearly impossible to control flight simulators. What truly makes this awful is that while flying itself was very straightforward and easy, the mandatory missions forced the player to use the poorest plane available. Imagine if the player had to do the street racing segments with a street sweeper, the slowest motor vehicle in the game.
 * RC Plane, Query Missions, Caesar's Races, Pilot School, rhythm sequences
 * Vice City had a boat mission with horrible controls. "It's time for the Lance Vance Dance", anyone?
 * Vice City Stories had the Boomshine Blowout mission, where you have to remove crates from a maze of a burning warehouse with a forklift.
 * In Dead Rising, the second-to-last part of the story suddenly puts you into a gun turret fighting off a tank. Then for the final boss you lose all your weapons and have to fight him with those hand-to-hand moves you probably never bothered to learn because a chainsaw always worked so much better.
 * I am an ex-outlaw being forced by the Army to kill my old running buddy for reasons unknown, and I am tasked with forming my own posse to take him down-but enough about that, let's race chariots!