Garlic (also known as Deranged Peanut Evolution) is a plant found somewhere in Wario's closet. If Wario happens to eat one of them, the chemicals inside the garlic can cause Wario's breath to be VERY horrible. If seen closely enough, they seem to have odd, smug, expressions on their faces, as if they had just eaten a human alive. They have also been found in Shigeru Miyamoto's office desk, to defend against intruders that might come in to steal his Mario cookies.
Garlic is said to ward off Boos, but this is a myth started by King Boo to trick foolish mortals into a false sense of security. Garlic is actually a power up that makes the undead feel three eons younger. Garlic also has other smell related properties. Some enemies can be warded away by the pure smell, but it often has to be eaten first (Wario is especially skilled with this power).