Not to be confused with Atomic Boo.
The Big Boo is a mini-boss fought in Paper Mario: Sticker Star. During the level The Enigmansion, Mario seals the Boos that inhabit the mansion into the Book of Sealing. However, after he does, Kamek releases them again. This time, they fuse together and become the Big Boo. During the fight, the Big Boo can only attack Mario by swallowing him, and spitting him out. Halfway through the fight however, the Big Boo will light some candles, making the room brighter and the Big Boo invisible. During this time, Mario cannot attack the Big Boo, but the Boo can attack him. In order to make the Big Boo vulnerable again, Mario must use a thing sticker that can extinguish the candles. The rest of the fight proceeds normally.