Purple

Purple is a freeware platformer game by Stanislav Stoyanov ("Rolling Cat").

The game is about a purple Waddling Head who escapes from prison with his Precision Quided Frisbee, only to meet Satan-lookalike thereafter who teleports him to a faraway land. That's pretty much what is there about the plot.

Purple draws, as the author states, inspiration from Super Mario World and the MOTHER series. There are 6 straightforward worlds with occasional Bonus Stages where player can earn 1-Ups and points. Each new level introduces a new gimmick to the game (either an old recolored enemy or an object appearing only once). There's also a dozen of various weapons for the player to find.

This game is also very hard. The author also made a (somewhat self-depreciating) playthrough for anyone who thinks it's too hard.

Tropes used in Purple include:

Acid Pools: In stage 2-5.
Adventure Towns: World 3
Auto-Scrolling Level: Stages 2-3 and 5-2
Background Boss: Mephistos after growing up.
Band Land: In stages 3-2 and 6-6.
Blackout Basement: Several caves are this, especially in night stages.
Bonus Stage: One for each world. You can enter them by pulling a hidden trigger in one stage.
Boss Corridor
Boss Arena Urgency: When fighting Mephisto.
Bottomless Pits
Breather Level: World 6 has much shorter stages than earlier worlds, and then there's Final Destiny.
Build Like an Egyptian: In World 4.
Cats Are Mean: In World 5, you can meet cat-shaped demons who throw explosive threadballs at you.
Cave Behind the Falls: If you find a waterfall, we advise you to enter it like a doorway.
Chain Lightning: The Zapper weapon.
Charged Attack: For every weapon you get.
Check Point
Continuing Is Painful: Choosing to continue the stage from the checkpoint will make you unable to earn 100% on that stage unless you start again from scratch.
Convection, Schmonvection: At one point you have to jump across platforms that rapidly dip into the lava.
Disconnected Side Area: Stage 2-3 has a chamber with a switch to Bonus Stage right above a room with a Check Point. The only way to reach the switch is somewhere in another stage.
Down the Drain: Stages 2-2, 4-2 and 5-4.
Drop the Hammer: One the most powerful weapons in the game.
Eleventh-Hour Superpower
Fireballs: You can throw them For Massive Damage.
Freeze Ray
Giant Space Flea From Nowhere: For a game where most bosses are humanoid, an eye on fire is rather... unexpected (unless you look into the game files).
The Goomba: Slimes
Goomba Stomp
Green Hill Zone: Stage 1-1
Gusty Glade: Seen around in World 5.
Harmless Freezing: The only thing Freeze Ray does is freezing enemies for a maximum of 3 seconds, unless it's a boss, in which case the freeze ray can only harm them.
Heart Container: You get one for defeating each boss.
Hearts Are Health
Heli Critter: The aqua-colored slimes.
Hell Hotel: Stage 3-3
100% Completion: Doing so may give you an award.
Hyperactive Metabolism: Averted. Picking up food gives you only points.
Ice Palace: Stage 5-5
Inconveniently-Placed Conveyor Belt
Interface Screw: Touching a certain object will cause the screen to shake and the left and right buttons to be reversed.
Invincibility Power-Up: The moon power-up.
Invincible Minor Minion: The barrel and trashcan enemies.
Kill Streak: Stomp multiple enemies without touching ground to rack huge points and eventually extra-lives.
Lava Pits: In stages 1-4 and 4-4.
Leitmotif: If Fresh Juice is playing, expect to see an Auto-Scrolling Level.
Load-Bearing Boss: Demonic and Flameye
Make My Monster Grow: Mephisto
Man On Fire: Frow World 3 and onwards, you can encounter people with burning heads (and later, freezing ones).
The Maze: Stage 4-4
Mirror Match: Right before the final boss.
Mirror World: World 6
Mutually Exclusive Powerups: Picking up one weapon discard the other.
Nintendo Hard: Expect to die a lot already on the first stage.
No Name Given: Everyone except for the bosses.
Number of the Beast: On the entrance to The Very Definitely Final Dungeon. You can even break it if you wish so.
Our Demons Are Different: They are humanoid and possess same weapons player can do.
Palmtree Panic: Stage 2-1 (no palmtrees though, just trees)
Pipe Maze: Not so much mazes however (there could be mazes, but all alternate routes are blocked off).
Precision Guided Frisbee
Product Placement: In 3-2, you can see advertisements for Coca-Cola and EarthBound.
Puzzle Reset
Random Encounters: On the world map, stepping on the blank node may result in a battle with a demon.
Recoil Boost: With Plasma Gun.
Rewarding Vandalism: Destroying TVs may yield out some goodies.
Save Game Limits: The game doesn't save progress you made within the world. It does, however, save the gems and records you got on each. The author admitted that it's horrible.
Scoring Points: There's even a highscore screen which stands out a lot from other menus, as a left-over from work-in-progress version.
Slippy-Slidey Ice World: World 5
Sound Test: With each track unlocked as the player first hears them.
Spikes of Doom: In three varieties. Short ones that merely hurt, long ones that kill instantly and retracting ones.
Spread Shot: Spread Frisbee
Springs Springs Everywhere: There are also green ones that mark the Level Goal.
Stalactite Spite: Icicles in World 5.
Super Not-Drowning Skills
Timed Mission: Almost every level.
Underground Level
Underground Monkey: Slimes come in four variations. Green (the basic one), orange (jumps), teal (takes off and flies) and yellow (leaves spikes when killed).
Underwater Boss Battle: Demonic can rise the water level in order to electrify you.
Vaporware: This game has been in development for at least 2 years before being released in August 2009.
The Very Definitely Final Dungeon
Waddling Head: Most characters in the game, including yours.
A Winner Is You
Where It All Began: The cell from the intro is where you also fight the final boss.
Wrap Around: In vertically scrolling areas.