A Bomb Boo is an explosive, black-colored type of Boo and enemy in Super Mario Galaxy. Bomb Boos appear in Ghostly Galaxy in the level Beware of Bouldergeist. Bomb Boos float lazily back and forth, exploding after some time, but moving towards Mario or Luigi upon seeing either one. They appear during the battle with Bouldergeist, who can only be harmed by having a Bomb Boo (or several) swung into him by the tongue using a Star Spin.