Boo Blah

A Boo Blah is a kind of ghost that appears in Super Mario World 2: Yoshi's Island and Yoshi's New Island. This creature sticks to the ceiling or the floor and jumps up periodically. They are generally invincible but are not a major threat, as they only hurt the player if they make contact with them while jumping up. Stomping them stuns them for a brief period of time and by holding the jump button, Yoshi can bounce off them. They can be defeated by using a POW Block or a cloud item. Also, there is an unused variant that has a Piro Dangle on it's head.

Trivia

 * They look incredibly similar to the Camo Goblin enemy that appears in The Legend of Zelda: Link's Awakening DX. They even share the same Japanese name.