Bug: Use Kirby and eat Yoshi so you copy his eating ability. Then eat Yoshi to turn him into an egg. The person playing as Yoshi must quickly mash buttons and the control stick to break out. When Yoshi is free, he will be smaller. This can be done over and over again, making Yoshi smaller and smaller. He can even get as small as a single pixel.
Other mistake: The Cloaking Device item helps nobody but CPU players. It renders a player almost totally invisible, and negates damage taken when activated. But players themselves can't see their own character when cloaked while CPU players have no trouble seeing them at all. Other than negating damage, the Cloaking Device is a poorly done item that only helps CPU players.