Ghast

The Ghast is a floating jellyfish-esque mob that shoot fireballs from its mouth. Its body is a 4x4x4 block cube with several tentacle-like body parts emerging 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 (5x5x5, occasionally 4x4x4; it is unknown whether this is a glitch or intentional). They are rumored to spawn near Portals in the regular world if given enough space to do so. Notch has confirmed this via Twitter, though he has said it is extremely uncommon.

Ghasts normally float around with their eyes and mouth closed, making a sound like giggling children. They open their eyes and mouth when attacking. They scream when shooting or taking damage. The sounds that ghasts make are currently not affected by distance, so they always sound very close, regardless of their actual position. They are said to be extremely difficult to handle when there are many of them.

The ghast's attack is a projectile fireball. The player can reflect the ball of flame by hitting it using anything, even your bare hands. Ghasts will not shoot at you if they cannot see you. They cannot see through glass or portals. Netherstone and imported Dirt blocks can be destroyed by the Ghast's fireballs. Netherstone will burn forever once struck. Stone buttons can also be destroyed. Materials that cannot be destroyed include, Cobblestone, Stone, diamond, Iron Doors, and Obsidian. If a ghast's fireball hits a portal (or close to it) the portal will be closed, requiring re-ignition, possibly by another fireball.

The ghast is not invisible, as was thought when it was first announced.

It can be hurt with normal weapons. Contrary to popular belief, ghasts can be set on fire, but will only be hurt for the duration of touching the fire/lava block it floats into. This also happens with Zombie Pigmen. It drops Gunpowder when killed, but this can be hard to collect - as it is the only mob that floats, the Gunpowder may fall into Lava or an inaccessible area.

It is interesting to note, flying creepers have been an "in joke" among the community, creepers that fly, and descend at the player to explode at them. It is possible that Ghasts were inspired by this joke, as they fly and shoot exploding orbs at the player.

Drops
Alpha:
 * 0-2 units of Gunpowder