Conflict Killer

You ever watch a show with a Conflict that suddenly gets derailed by a relatively minor or previously unseen character who suddenly becomes the Big Bad and derails the conflict you were previously enjoying? That new villain is the Conflict Killer. They come in and replace the existing plot with a completely new conflict, often by causing the hero and previous villain to put aside their differences and face the new threat, earning a new respect for each other and frequently never getting back to the conflict we were watching in the first place. This isn't necessarily negative, however, as sometimes a conflict killer is a Magnificent Bastard who takes the work to another level.

Distinct from The Man Behind the Man because this villain was either heretofore a minor player or had no previous role in the story.

Occasionally overlaps with The Worf Effect when the new villain shows off their might and the Sorting Algorithm of Evil when the Conflict Killer is clearly more powerful than the previous villain. Sometimes the new villain is conveniently Black in terms of evil, as opposed to merely Gray like the previous villain, and kills the previous villain off.

Compare Plot Tumor and They Wasted a Perfectly Good Plot. If this happens in a video game it may result in a Bait and Switch Boss, but only if said boss is driving the plot. Contrast the Giant Space Flea From Nowhere that appears with no explanation. If the mystery surrounding him and/or the existing players' ignorance of him are plot points, this is Outside Context Villain instead. This is a spoiler heavy trope, so read on at your own risk.

Anime and Manga

 * The entire premise of Strike Witches for World War II. Instead of World War II being fought against each other, it's against the Neuroi Alien Invasion.
 * Kyoji Mujo from S-Cry-ed managed to take over the story entirely, burying the whole Kazuma vs. Ryuho rivalry until the final episode.
 * Same with the Overdevil from Overman King Gainer. The final scene of the series is practically a Lampshade Hanging: "er, guys, weren't we supposed to be headed to Yapan instead of dealing with Eldritch Abominations?"
 * Piccolo and Son Goku's rivalry in Dragonball Z effectively ends when the arrival of Raditz, Nappa, and Vegeta force Piccolo into a Heel Face Turn.
 * Also, Cell, who was introduced shortly after the androids were introduced, ends up becoming the big bad of the current arc.
 * Vegeta later teams up with the heroes to take on Frezia and the Ginyu Force.
 * The Water Seven storyline of One Piece seems to set up Franky as that arc's big bad by having him and his goons beat Usopp to a bloody pulp. The Strawhats vow revenge and tear Franky's henchmen a new one, causing HIM to swear vengeance in turn...it all seems to be leading up to a big showdown between Franky and Luffy, until the Wham! Episode which turns the plot on its head leaves our heroes with much, much bigger problems to worry about. Franky does a Heel Face Turn and proves to be far more interesting as a good guy, anyway.
 * In Mahou Sensei Negima, this is how Tertium treats the . An unusual villainous example since to the heroes, this doesn't make a lick of difference, they're still fighting for their lives against impossible odds.
 * In Alive the Final Evolution, the three way conflict between the American government, the alien Mitama and her followers, and the protagonists over possession of the "Heart of Akuro" gets derailed near the end by Hirose, who was given the Heart on the assumption that he could be easily manipulated. With the Heart making him the strongest thing on the planet, Hirose ignores the secrecy all the other factions were fighting under in favor of single-handedly launching a war against everyone else on the planet. The previous conflict between everyone is put aside in order to stop his attempt to commit genocide on all of humanity.

Comicbooks

 * In Transformers Generation 2, it seems like the coming of the Swarm (hinted by visions Optimus Prime had) will end the conflict between the Autobot-Decepticon Alliance and the Cybertronian Empire, but the trope is averted when Optimus tries to reason with Jhiaxus to work together against the Swarm, since Jhiaxus responds trying to kill Optimus. Besides, after Jhiaxus dies and the menace of the Swarm is over, the Cybertronian Empire still exists at the far reaches of the universe, led by The Liege Maximo.

Fanfic

 * from (On the) Path of Vengeance, possibly reprising this role in Endless Waltz.

Film

 * In The Matrix movies the conflict between the machines and humans is derailed by the resurrection of Agent Smith who becomes the Big Bad despite because of Neo deleting him at the end of the first movie.
 * Then again, the ultimate result of this is for a solution to be found for the original conflict, not to just push it aside. The plot around Smith is just another thread in the conflict of humans versus machines; the happy ending is all about the latter being (sort of) resolved.
 * In Changing Lanes, the two man rivalry between Ben Affleck and Samuel L. Jackson is put aside when they both decide to go after Sidney Pollack, thus eliminating the violent escalations that defined the movie up to that point.
 * In Hancock, after Hancock gets rehabilitated and stops a bank robbery, he starts to get uncomfortably affectionate with Mary, the wife of The Everyman who helped him put his life together. It is about to turn unspeakably ugly - how can you stop or arrest a superpowered rapist? - when . See Hancock for more on the original script, which was regarded as unfilmable for this reason, among others.
 * Cowboys Versus Aliens begins with a fairly standard Western conflict between a cattle baron and the local law, but gets derailed by the sudden appearance of aliens. The two sides join forces to attack the aliens and renconcile their differences.

Literature

 * The Culture novel Matter:
 * One of the main themes in Matter was inter-galactic politics and interactions between different tech-level species. The inheritance conflict was very important to the people living in the empire, but insignificant to the rest of the galaxy. The whole thing was set-up as a Wham! Episode to show how none of it really Mattered in the end.
 * Isaac Asimov's Foundation series has the Second Foundation attempting to shorten the length of time the Empire collapses to a thousand years when "The Mule" arises, derailing the Plan-scheduled civil war by having the Traders and Foundation proper join up against the threat of the Mule.

Live Action TV

 * In the fourth season of Buffy the Vampire Slayer,
 * Buffy Season 2 did this twice. Season 1 ended with the Anointed One, a sort of Vampire Messiah in a child's body set up as the new Big Bad. That was awesomely undone when Spike showed up and started his plans to reassemble The Judge. Spike vs. The Slayer was later taken over when Angelus appeared in the middle of the season.
 * Also happens when in Season 6. Buffy is fond of this trope.
 * Happens yet again in season three, with Mr. Trick, a clever vampire crimelord who gave Buffy a great deal of trouble early on in the year, getting abruptly staked by Faith, just in time for her and The Mayor to step in as the real villains of the season.
 * By then Mr. Trick had already become The Dragon for The Mayor, Faith just replaced him in that role.
 * In the third season of Deadwood, Hearst enters town and forces an uneasy alliance between Bullock and Swearengen.
 * Happens in Stargate SG-1 when the Replicators start destroying the Goa'uld, suddenly fixing the problem the heroes have been dealing with for the past 8 seasons. This also forces them to work with Ba'al to destroy the Replicators, but they go back to being enemies shortly thereafter.
 * Occurs in Stargate Atlantis when the Replicators start to attack the Wraith by attacking humans. Atlantis teams up with Todd and his Wraith to destroy the Replicators, but, as with the SG-1 example above, they do resume their regularly scheduled conflict once the Replicators are dealt with.
 * Arguably an inversion: In Star Trek: Deep Space Nine, the introduction of the Dominion rapidly took over the entire series, spanning the entire rest of the show's run at the expense of most episodic plots.
 * Played straight in the final episode of the second season of Star Trek: Enterprise. The Xindi take over the story for the next full season.

Tabletop Games

 * Warhammer 40000 was originally a conflict between the Imperium, the Forces of Chaos, Orks, Eldar and Tyranids. Then in the 3rd edition they added two armies, the Dark Eldar and the Necron and attempted to cram the Necrons in as the new Big Bad. Games Workshop also attempted to add the Necrons in as a mysterious, subtle horror, which doesn't always work in a universe about as subtle as being bludgeoned with a GWAR concert.
 * This said, it has to be taken as a growth from being Warhammer INSPACE! to being it's own work. The game is a far cry from being Rogue Trader. (The original game, not the RPG)

Video Games
"Vergil: Well, you don't possibly believe that he deserves to be our main event, now do you?"
 * In Legend of Dragoon
 * Subverted and Lamp shaded in Command and Conquer with the introduction of the Scrin, who note that the two factions (Nod and GDI) are continuing to fight each other while battling the Scrin invasion.
 * Martinez in Grand Theft Auto: Vice City Stories is an annoying example, where he interrupts the plot near the end, thinking that the player is the same nobody he pushed around in the beginning, despite the player at this point having taken out Martinez' boss' boss' bosses, and can buy and sell his entire racket millions of times over.
 * Arkham from Devil May Cry 3, even though the brothers teaming up was one of the series' (many) Crowning Moments Of Awesome. Vergil later Lampshaded it:
 * Arkham from Devil May Cry 3, even though the brothers teaming up was one of the series' (many) Crowning Moments Of Awesome. Vergil later Lampshaded it:


 * Star Ocean: Till the End of Time. Fayt is stranded on a backwater fantasy planet with no way off, and the main conflict is a fairly standard fantasy world war between religious matriarchy Aquaria and hostile, warlike Airyglyph, until
 * You could say there was a second Conflict Killer in 3, but that wasn't the part that was not well-received, and it wasn't really a Conflict Killer quite so much.
 * Jie Revorse in Star Ocean 1 for SNES/SFC. In the PSP remake, this is much better handled and explained and he no longer comes out of nowhere.
 * In Jak 2 Renegade the main villain at the start is set up as baron Praxis, who Jak has sworn to get revenge on. They fight twice, but the Baron is never really defeated. Near the end, he is killed by the real Big Bad, the metal head lord.
 * Final Fantasy VI spends the first half of the game focusing on the conflict between The Empire and the Returners, before Kefka, formerly The Dragon, reveals that he has his own apocalyptic ambitions. The Emperor belatedly tries to stop him, but Kefka proceeds to settle the the conflict by destroying both sides, along with most of the world, and setting the stage for a final showdown with him instead.
 * Final Fantasy VII would go on to use much the same plot structure. The first part of the game seems to be a struggle between La Résistance and an evil Mega Corp. Once Sephiroth shows up and goes on a killing spree through Shinra's headquarters, though, the story quickly switches tracks and he becomes the new Big Bad. The Corrupt Corporate Executive even went on to pull a Heel Face Turn in the spinoff games, due to Sephiroth being so much more evil in comparision.
 * Final Fantasy X seems like a straightforward pilgrimage to gather all the Aeons and defeat the Big Bad Sin. At least until Maester Seymour goes right off the rails midway through the game and you find out that he's been an Omnicidal Maniac all along who wants to take over Sin and use it to destroy Spira. Getting back to the matter at hand and finishing Sin off seems almost like an afterthought once Seymour's finally out of the way.
 * Tales of Vesperia. One word: "Adephagos." Turned a perfectly good ethical conflict into a "stop the Knight Templar and the big bad monster thing" race with a final dungeon that came out of nowhere.
 * Maybe. Though it should be noted that a major theme of the game is that peoples choices have consequences; someone has to deal with them, even if you don't. It could be argued that the last third of the game is dealing with the consequences that others did not face.
 * Fate/stay night has several over the course of its three storylines. First, in the Fate route, Gilgamesh takes out Caster during Caster's sudden attack on the heroes' base and establishes himself as the new villain (he actually turns out to be The Dragon). Then, in UBW, Archer takes out... Caster... when she's about to kill them. And then... Gilgamesh kills him shortly afterward when it turns out that Archer may not be all that bad. Finally, in Heaven's Feel, the Shadow and True Assassin practically ruins the whole Grail War by dropping bridges on all the Servants except Rider. The one that the heroes first discover? Caster.
 * In Fire Emblem 10 (Radiant Dawn), Part 3 is a war embroiling most of the known world, stopped short by the awakening of a god. It had been foreshadowed since the previous game that such a war would cause this to happen, and comes right in time since the player controls both sides of the old conflict.
 * The beginning of Super Mario RPG, where instead of a normal "Mario defeats Bowser" story, the two rivals join forces to defeat a giant sword.
 * All three Mario & Luigi games begin with Mario battling Bowser in Peach's Castle to stop him from kidnapping her, just before they find out about the true villains.
 * Early in Clash at Demonhead, you have an inconclusive fight with Tom Guycot, the apparent boss of the terrorist organization you're trying to defeat. About halfway through the game during a seemingly-unimportant sidequest, the player character is tricked into releasing a demon. Said demon promptly clobbers him and kills Guycot, forcing the player to go on a quest for a magic sword to kill the demon. You'd think the demon would then take over the plot, but in a weird subversion, you just kill it with the sword,  then go right back to fighting terrorists. The Final Boss is the guy who was giving Guycot orders.
 * The first Starcraft campaign concerns the conflict between La Résistance and The Empire. Then the Zerg show up.
 * A common phenomenon in many strategy games (particularly of the Four X type) which involve multiple competing sides and a Tech Tree. What happens is that while the more active players expand and compete with each other militarily, a less aggressive faction is able to sit back in their corner of the map and climb the Tech Tree undisturbed. This eventually gives them an unstoppable advantage over the apparently superior competitors when they do join in the fray. Occurs less often in multiplayer games, as humans know to team up and gank the techer early on.

Web Comics

 * Morgan takes over Troy's role as the Big Bad when the characters' masks start to come off. Because he is hideously disfigured (chemical splash at college), he refuses to allow people to be different and forces people to wear masks like he does.
 * 8-Bit Theater has what looks like a final conflict brewing between the Light Warriors and the Dark Warriors; but then the Other Warriors show up because they want to kill the Light Warriors too; but then, the Fiends show up to kill the Light Warriors as well, so they look like the BigBads; but then Black Mage Anticlimactically absorbs their power for himself which makes it seem as if he is the Big Bad; but then Sarda reveals himself as the Big Bad, (although he actually claims that the Light Warriors themselves are the BigBads); but finally Sarda blows up due to absorbing too much power, and becomes a portal for Chaos' who is the actual Big Bad. All in all there are five Conflict Killer moments in succession at the end of the comic.

Western Animation

 * Chaotic's second season has a fifth tribe, M'arrilians, appear and change the plot from the previous search for the Cothica and fights between the tribes to the tribes working together to fight the new threat.
 * The main conflict of the first season of Avatar: The Last Airbender revolved around Prince Zuko following the Gaang around the world trying to capture Aang so that he could return from his exile, accompanied by his uncle Iroh. The second season opens with his sister Azula (who had previously only be seen in passing during a flashback and recieved a brief mention in the last episode) attempting to arrest the two of them, forcing them to go on the run. Shortly after, Azula encounters Aang by chance and resolves to track him as well. Only one episode has Zuko still trying to capture Aang, and he still has to compete with Azula to do it. A bit more palatable then usual, as the first season had clearly ended on the fact that Zuko and Iroh had become vilified by the Fire Nation, as well as having lost the resources which would let them follow the Gaang.
 * Re Boot subverted this. When the Web invades Mainframe Bob and Megabyte are forced to team up. Instead of ending their conflict, Megabyte takes advantage of the situation to get rid of Bob before the Web invasion is over.
 * "Family Guy" had a joke poking fun at this. At the beginning of "Brian Griffin's House of Payne," Peter mentions an idea he has for a "Jaws" sequel where the humans and the shark team up to fight an even bigger shark, named "Big Jaws." At the end of the episode, we find out he got it produced, and get to watch the scene introducing the Conflict Killer in question. Not surprisingly, it's awful.

Real Life

 * The British to the Muslims and Hindus in India.
 * In 1244, the Mongols sacked Jerusalem.
 * Err, no. It was the Khawarezmi Turks that did it. They were wondering across the region after having been displaced from their original territory by the Mongols when the Egyptian Sultan decided to hire them to secure the region, and they sacked the then christian-held city on the way. The Mongols did later venture into the area, but whether their raid ever penetrated the city was arguable and even if they did the effect was insignificant.