The Bomb Boo is an unusual Boo variant that appears in Super Mario Galaxy and Super Mario Galaxy 2. They are black instead of white, with yellow eyes and fangs. They are much more daring than standard Boos as they will attack even when Mario is looking at them. Worse, as their name suggests, Bomb Boos will explode when they close in, flashing red moments before detonating.
In both Super Mario Galaxy and Super Mario Galaxy 2, Mario encounters Bomb Boos while battling the boss Bouldergeist. Mario needs the Bomb Boos to defeat Bouldergeist; when a Bomb Boo is close, Mario can use his Spin Attack and grab a Bomb Boo by its tongue and swing it around, slamming it into Bouldergeist's rocky body and causing the Bomb Boo to explode on impact, damaging the Bouldergeist in the process.