The Boo Mushroom is a power-up from Mario bros series. It is a Mushroom that resembles a Boo a species of ghost. a boo a spherical ghost with menacing mouths with sharp teeth. They are known for their large tongues and small stubby arms.

When someone eats the Mushroom, they become a Boo in a matter of minutes. Its a painful, yet.. oddly nice feeling. Although they become a ghost, they don't die.