Big Boo

Super Mario World
They appear in ghost houses, having a frown.

Hotel Mario
They appear in Ludwig von Koopa's hotel, 1/6 as big as the hotel.

Yoshi's Safari
They appear as a boss when shot, it seperates into 3 smaller Boos. Mario must shoot the Boo with a tongue.

Super Mario RPG:Legend of the Seven Stars
One Big Boo appears in a cameo.

Super Mario 64
Big Boo is a boss in Super Mario 64 and the remake for the DS. He appears in the level Big Boo's Haunt and was faced many times over the course of the level the final showdown was on the balcony of his house. The Big Boo is the leader of the Boos in Super Mario 64 DS.

Paper Mario: The Thousand Year Door
They are named Atomic Boo. Their stats are 40 H.P., 4 Attack, and 0 Defense.

Super Paper Mario
Atomic Boos are very rare. They try to attack Mario by sneaking without being looked.

New Super Mario Bros. Wii
They reappear in the ghost houses again, but they can`t stop attacking until all players look at it.

Super Mario Galaxy 2
They cannot stop following Mario until Mario is close for a Power Star or a Launch Star, or he looks at them.