Balloon Boo

Balloon Boos are large relatives to Big Boos that appear only in New Super Mario Bros., encountered in World 4-Ghost House. They are large Boos with pink cheeks and their tail is that of a balloon's. When they are not looked at, they will persue the player, releasing the air, and reduce in size; giving the player the chance to pass through. When looked at, they will inflate by sucking in air, gaining size until large enough. They will still chase Mario or Luigi, even when they have no air left. Balloon Boos can be defeated with a Blue Shell or a Mega Mushroom. They will only attack the player when the heroes are in the same room as they are.

Trivia

 * When Mega Mario or Mega Luigi runs into a Balloon Boo, they pop and fly away in circles.