Bouldergeist

Bouldergeist is a boss in the game Super Mario Galaxy. Its name is a pun on boulder and poltergeist. It is the boss of the Ghostly Galaxy, and may or may not be based on Eyerok from Super Mario 64.

Appearance
Bouldergeist is essentially a huge column of rocks roughly shaped into a face. However, its real form is a more extreme version of a Bomb Boo, with what could be its uvula, tongue or heart hanging from the bottom. It has two enormous stone hands, which are used only in the second half of the battle. Bouldergeist's attacks include tossing rocks at Mario, summoning lines of stalagmites from the floor, and in the second half of the battle, slapping his hands on the ground and punching at Mario. It is fought in a plain circular arena.

Combat
To defeat Bouldergeist, Mario must swing Bomb Boos into it. Each hit will gradually cause Bouldergeist to lose a bit of its stone layer. Three hits will completely destroy the entire stone layer surrounding Bouldergeist's real form. Once this happens, Mario has to, yet again, spin a Bomb Boo at the shadow's red bubble to inflict more damage on Bouldergeist. However, the fight is not over, as Bouldergeist regains its old stone layer, and reveals its large rock hands. Bouldergeist then has a greater variety of attacks, as well as a larger form of protection. Mario can, however, destroy the hands the same way, but they regenerate after a short time, so Mario has to damage Bouldergeist before the hands reappear again. Mario must once again swing three Bomb Boos into it, and then swing one final Bomb Boo into its shadow form to defeat the malevolent stone creature and claim his Power Star.

Trivia
The theme music while fighting Bouldergeist is the same as Kingfin's theme music.