Ghast

"At least they keep their eerie red eyes shut. Until the Ghast learns you're around, of course."

- Tom Stone

Ghasts are huge, floating hostile mobs from the Nether that shoot explosive fireballs at the player, and are the second largest mobs in the game, the largest being the ender dragon.

Spawning
To spawn naturally, ghasts require a solid block below them and 5×4×5 free space in order to spawn, and only spawn in the Nether, in any light level. In a single chunk only one ghast can spawn at once, although due to pack spawning the game tries to spawn up to four entities. They sound like ur-ghasts as well.

Ghasts will not spawn in nether fortresses.

Drops

 * 5 experience points when killed by the player

Behavior
Ghasts normally float around the Nether with their eyes and mouth closed and periodically make high-pitched, cat- or infant-like sounds. They open their red eyes and mouth when attacking. They make a screaming noise when shooting and scream pitifully when taking damage. The sounds that ghasts make have a minimum intensity regardless of their distance, meaning that they can sound closer than they actually are. They have a size of 4×4×4 blocks, as well as 9 tentacles about the size of a player, although longer and skinnier. However, the tentacles are not part of the ghast's hitbox.

Ghasts have an extreme attack range (up to 100 blocks), explosive attack power, and mobility. Unlike most other aggressive mobs, the ghast does not have a pursuit mode - it does not attempt to draw closer to the player when at long range (and likewise is not particularly likely to float away). Ghasts can cause other mobs to attack it, but the ghast will never target other mobs; it will only target the player. Compared to other mobs, the ghast has a very long search range and can target a player from up to 100 blocks away. When the player comes within about sixteen blocks, the ghast will turn to face the player, open fire and attempt to gain altitude but will fly away when hit in Creative.

Ghasts will not fire at the player without a line-of-sight, which can be blocked by solid transparent blocks.

If the player is able to fly inside an aggressive ghast, the mob may die of shooting fireballs at itself. They are also careless about shooting at short range where they will be hurt by the blast.

Wither
Ghasts are the only non-undead mobs that the wither will not attack.

Data values
Ghasts have entity data associated with them that contain various properties of the mob.

Ghast fireball
The ghast's fireball attack has a straight trajectory unaffected by gravity and a theoretically infinite range, though it will disappear after 1 minute. Fireballs do not track the player once fired, are slow, and can be deflected if the player hits them with a projectile, fishing lure or melee attack. At close range, it is one of the most powerful mob attacks in Minecraft, fourth only to the explosion of a creeper, the melee attack of an iron golem, and the explosion of a wither. A direct hit will deal projectile damage from the impact, and up to, , or  explosion damage from the blast, depending on difficulty. When two ghast fireballs collide, one is deflected to a random direction while the other explodes upon impact. Blocks are also set on fire by the explosion. If a ghast is killed, any fireball launched by that ghast will disappear. A fireball will deal 1,000 damage (500 hearts) to a ghast if the fireball was rebounded by a player.

The minimum blast resistance required to absorb all blast force of the ghast's fireballs is 20.17 (about the equivalent of a cobweb). Ghast fireballs therefore cannot damage cobblestone, which has a blast resistance of 30.

Entity data
Ghast fireballs are also entities which have associated entity data.

Trivia

 * The player can go inside of a ghast by falling through the top of it or flying up underneath it. If the player stands on top of the head, the player will see inside of it.
 * If a ghast is trapped in a 1-thick cube, it will shoot fireballs through the cube. This is because all mobs that shoot spawn the projectile one block in front of it to prevent the projectile from hitting the mob.
 * On rare occasions, a ghast will spawn in such a way as to see through blocks (usually trapped on all sides in a tight area). When this happens and the ghast has “line of sight" through those blocks, it will launch a fireball in the player's direction.
 * Ghasts can be killed in one shot by any bow with at least Power I, if you charge the bow fully.
 * C418 revealed in an AMA on Reddit that ghast sounds are taken from his pet cat, which he makes when disturbed while sleeping.
 * Two ghasts are featured in the LEGO set "Minecraft Micro World - The Nether", along with a Zombie Pigman.
 * Iron golems do not fight ghasts unless they are very close to them, even in this case it's rare.
 * When killed with its own fireball, the ghast will turn orange rather than red. This is because the ghast is set on fire.
 * Splash potions will only affect ghasts when hitting them on their lower half.
 * Despite not having visible feet, ghasts are still capable of making footstep sounds.
 * In snapshots 13w02a (for 1.5) the fireball texture was replaced with a diamond helmet.