Balloon Boo

Balloon Boos are enemies that have only appeared in New Super Mario Bros., where they are only encountered in. They are Boos with pink cheeks, and their tail resembles a balloon knot, akin to their name. The level contains five Balloon Boos; thus, only five appear in the whole game.

They appear large at first, but when looked away from, they approach to the player while expelling air and shrinking; otherwise, they stop and inflate by inhaling air at a rather slow rate, until it has assumed its massive appearance once more. Balloon Boos will continue to chase Mario or Luigi even when they have reached their minimum size. Balloon Boos can be defeated with a Blue Shell or a Mega Mushroom.

Trivia

 * When Mega Mario (or Mega Luigi) comes into contact with a Balloon Boo, it flies away in a circular motion, similar to a balloon propelling air erratically when it is released.