Boo Balloon

A Boo Balloon, also known as a Blue Boo, is a Boo in the shape of a blue balloon in Super Mario World 2: Yoshi's Island. They race about the screen, trying to deal damage to Yoshi. They will inflate when hit with a Yoshi Egg. After three hits, they will explode, yielding coins or sometimes a ! Switch.

Trivia

 * The Nintendo Power SNES guide erroneously lists Blue Boos as separate from Boo Balloons, with Blue Boos exclusively appearing in Bigger Boo's Fort; however, they are the same enemy, and as such also appear in Don't Look Back! This is likely due to the fact that the string isn't visible due to the background being black.