Boos are enemies seen in the 2009 Mario fangame Super Mario 63. They are members of the Koopa Troop and are led by King Boo. Their main method of attack is following Mario from behind. If Mario turns around, they'd stop moving and turn invisible before Mario turns his back on them. They're also invincible as Mario can't kill them in any way whatsoever.
Biography[]
In "Big Boo's balcony", when Mario first enters the house, King Boo mocks him that he had scattered multiple keys across the mansion and has sent his minions to go after him. When Mario collects all of the keys, he goes to the top of the titular to get the Shine Sprite.
In ""Switch" to the secret room", King Boo tells Mario to not press the ghostly Green Switch because it'd put a curse on him, just to make sure he doesn't get the Shine Sprite. When that fails, Boo sends his minions to take care of Mario for him.
If Mario goes into the mansion's basement, he'll be greeted by a seemingly unguarded Shine Sprite. When he tries to reach it, King Boo will show up and close the windows and the entrance to the basement, triggering a boss fight with him. Other Boos show up to aid King Boo during the fight alongside purple Cheep Cheeps.