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Two Big Boos around Mario.

Big Boos are ghost enemies that appear in Ghost Houses in New Super Mario Bros. Wii. Big Boos are a large sub-species of Boos, being 3 times bigger than the normal Boos. They act the same way as a Boo. When Mario and the crew (Luigi, Blue Toad, Yellow Toad) face them, they cover their faces. When Mario turns his back on them, they follow him. Big Boos are harder to dodge, due to their enormous size. If Mario touches a Big Boo, he takes damage. Big Boos, like normal

Four Boos in a Big Boo chase Mario in the Haunty Halls Galaxy of Super Mario Galaxy 2.

Boos, glow in the dark. Big Boos are the largest Boos in the game. They don't appear anywhere else, but the Ghost Houses. That means you only encounter Big Boos in the Ghost Houses. The only way to defeat a Big Boo is to touch them while under the effects of the Starman. Unlike regular Boos, the Big Boo will not stop pursuing unless all players are looking at it. Big Boos reappear in Super Mario Galaxy 2 in the Haunty Halls Galaxy. They only appear in the galaxy's second mission, Sneaking Down the Creepy Corridor. Here, they appear twice. When they appear, the Big Boo appears along with four regular Boos. It is in the middle of the other Boos, "showing its great size". The Big Boo and its four Boo "friends" chase Mario/Luigi down the hallway and down the last part of the Halls Galaxy#Conveyor Belt Planet Conveyor Belt Planet. They will not stop chasing Mario/Luigi unless they are looked at or if Mario/Luigi reaches a Launch Star/collects the Power Star. In this game, Big Boos cannot be defeated. Big Boos also appear in Super Paper Mario under the name "Atomic Boo". They are rare enemies, for only one appears in Merlee's Mansion. It attacks the player by attempting to charge at them when the player is not facing them. It will become shy and invisible if looked at. They also occasionally appear in the minigame of the Arcade, Mansion Patrol. They are slower than regular Boos and take several hits to defeat.