Big Boos are recurring ghost enemies from the Mario series that stalk people and live in The Castle and the haunted house. They are bigger versions of normal Boos. Mario dies from having a staring contesst with one in 101 to kill Mario (the right way). Another one appears in Luigi's Retarded Mansion and say's "Dat Ass", scaring Luigi. It also appeared in Rich Glitch where he helps SMG4 and the gang to get in Mario's house.