From the Super Mario Wiki
A Boo Blah is a kind of ghost that appears in Super Mario World 2: Yoshi's 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.
Names in other languages
- ^ Super Mario World 2: Yoshi's Island Nintendo Player's Guide. Page 126.