Balloon Boo

Balloon Boo is a Boo appearing in the Mario series who exclusively appears in New Super Mario Bros. in the World 4-Ghost House. They inflate when Mario or Luigi stares at them and grows bigger and all of its air will run out when Mario or Luigi look away from them and they will decrease and look like a regular Boo. They don't notice Mario or Luigi unless they enter their area, unlike Boos. They can be defeated only by a Mega Mushroom or a Blue Shell.