Spawn Egg

A Spawn Egg is an item that may be used to spawn mobs directly. It is available to regular players in Creative Mode and to server ops in both Creative and Survival Mode. It allows the player to spawn a variety of mobs on command, although some mobs are not available in Item Selection for certain reasons.

Use
A Spawn Egg is used by right-clicking on a surface with the egg. The egg's mob will appear with its feet immediately adjacent to the surface. Unlike Chicken Eggs and Ender Pearls, Spawn Eggs are not thrown; the player must be within normal range of the block. Hostile mobs spawned while on the Peaceful difficulty setting will instantly vanish, just like mobs from Monster Spawners.

As of Pre-release 12w03a, eggs can be placed into a dispenser. Activating the dispenser will spawn the mob instead of dispensing the egg.

Spawn Eggs on Survival Multiplay (SMP) Servers
Spawn Eggs can be obtained by ops using the SMP Command /give. When using this method, the damage value of the egg spawned pertains to the Entity ID of the entity it makes. Not only does this allow the player to spawn unavailable mobs such as Giants, it allows them to spawn other entities, such as Minecarts or even Primed TNT. These eggs will be the default color, white with grey spots.

The format for the /give command is:
 * /give PLAYERNAME 383  
 * Example: /give PLAYERNAME 383 1 120 would give a player a single Villager Spawn Egg.

Note: Spawning entities that require extra data (such as paintings) will cause the game to crash.

History
Spawn Eggs were added in the weekly Pre-release 11w49a and later included in the 1.1 Official Release.

Trivia

 * In 12w01a, the egg and its markings had their textures separated in order to allow them to have entirely different colors. This allowed their colors to be changed to better suit the mobs themselves.
 * Mobs spawned via this item act the same as normally spawned ones. As such, hostile mobs will despawn if the player ventures too far.
 * The use of dispensers to spawn mobs was first seen in the prerelease screenshot 12w03a.
 * In 12w03a the Spawn Egg is stackable.