Air Bag

From the Super Mario Wiki

Air Bags are giant, purple balloons that appear out of Mystery Crates. They attack by blowing air at Yoshi. An Air Bag may be revealed by shooting an egg at an unmovable crate. To defeat one, Yoshi must throw an egg at the bandages on its belly. The reward for defeating an Air Bag is a Melon. Air Bags only appear in Yoshi's Story, and even then only in 1-2 Surprise!!