Super Smash Flash/YMMV

• Game Breaker: Yoshi in the second game's v0.8a demo. Good at racking up damage, powerful smashes, and his Egg Lay can kill you if used off the edge.
• Goddamned Bats: The Buzzers in Race to the Finish in Super Smash Flash. There are a lot of them, they know exactly where you are, and they will run into you over and over again till you fall to your death. At best, they'll delay your progress a bit, which wouldn't be so bad if this weren't Race to the Finish.
• Good Bad Bugs: In the first game, a bug allowed you to skip any level in the game (except Target Test), making unlocking the full set of characters much easier.