Boos are ghost-like creatures that appear in the Mario franchise. They are typically found in dark areas, such as haunted houses and castles. Boos are very shy and will often hide from Mario. However, if they are spotted, they will chase Mario and try to scare him. Boos can also possess objects, such as paintings and blocks, to surprise Mario. Boos are weak to fire and can be defeated by being stomped on. However, they can also be defeated by collecting a Starman power-up, which makes Mario invincible. Boos are a recurring enemy in the Mario franchise and have appeared in many games, including Super Mario Bros. A fanart Super Mario progress bar for YouTube with Mario Boo.