|Game(s)||Newer Super Mario Bros. DS|
|First appearance||(DS) The House of Blocks|
|Final appearance||(DS) The House of Bogus|
Balloon Boos appear to be bigger, chubbier Boos. They have an uncomfortable expression, along with bright pink cheeks, which is one of the defining features of the Balloon Boo. It gets smaller while chasing the player.
Balloon Boos act a bit similar to normal Boos. When you look at them, they'll stop and stare. Meanwhile, when your back's turned, they'll follow you while slowly losing air and getting smaller. When they get to about the size of Mario, they'll stop shrinking. Once you turn around and face them, they'll start sucking up air until they go back to their original size.
There are also some stationary Balloon Boos, who just stay there and look in one direction. These Balloon Boos will do nothing, so you must just jump over them or somehow get around them. Balloon Boos can't be killed by most things.