Boo Balloon

A Boo Balloon 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 an egg. After three hits, they will explode, yielding coins or sometimes a ! Switch. They appear in Bigger Boo's Fort and Don't Look Back!, with the former called Blue Boos in the Nintendo Power SNES guide due to the black background rendering the string invisible.

Super Mario World 2: Yoshi's Island

 * Shogakukan guide: 風船みたいにふわふわ浮かんでいる. 急降下で襲ってきたら、舌をのばして追い返そう. (They float around like balloons. If they swoop down and attack you, stretch out your tongue to send them away.)
 * Player's Guide (Blue Boo): They only flutter in the darkest chamber of Bigger Boo's castle. Hit them with three eggs.
 * Player's Guide (Boo Balloon): If he could, Boo Balloon would get a mowhawk and a bunch of tattoos to show what a toughie he is.

Yoshi's Island: Super Mario Advance 3

 * Shogakukan guide: 風船みたいにふわふわ浮いている. 急降下でおそってきたら、舌をのばして追い返そう. タマゴを３回当てると倒すことかできる. (They float around like balloons. If it swoops down on you, stretch out your tongue to drive it back. If you hit it with an egg three times, you can defeat it.)