Ghast

Ghasts are large white jellyfish-styled mobs that dwell only in The Nether. They float through the air and shoot fireballs from their mouths at the Player. Their bodies are 4 by 4 by 4 block cubes with 9 tentacle-like limbs hanging from the bottom. They first appeared in the Halloween Update. Ghasts are able to spawn anywhere in The Nether, as long as there is sufficient space (5*5*5 space is required to spawn) and the game is not in Peaceful mode. If they are spawned in an insufficient space, they will suffocate - quickly.