Some Boos and a Balloon Boo.
Balloon Boos are similar relatives to Big Boos that appear only in New Super Mario Bros., encountered in World 4-Ghost House. They are Boos with pink cheeks and their tail resembles a balloon's instead of a ghost's. They will appear large at first, but when ignored, they will approach to the player, while expelling air and shrinking; allowing the player to take advantage to progress. When observed, they will stop and inflate by inhaling air at a rather slow rate, also growing, until it has assumed its massive appearance once more. They will proceed 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. Unlike regular Boos however, they will react to the Mario Brothers, only when they are in the same room.
- When Mega Mario or Mega Luigi collides with a Balloon Boo, they pop and soar away in circles, somewhat reminiscent to knocking out a Goal Pole.
- A similar species in New Super Mario Bros. 2, called the Boohemoth, has a small resemblance to a Balloon Boo, but does not act like one.