Invisible Wario

Invisible Wario is just one of Wario's many, many transformations in the Wario Land series of games. When hit by a certain potion thrown by Mad Scienstein, he turns completely invisible, including the player. The only way to figure out where he is is the occaisional cloud of dust by his feet, or the scrolling of the screen as he walks. However, it is needed to pass usually protected doors guarded by large eyeballs, as Wario cannot be seen. This is one of the only cases where in-game invisibility is a hinderance to the player, instead of a useful ability.