Shulker

Shulkers are hostile mobs that are found in the outer islands of the End. They hide in their shell to blend in with surrounding purpur blocks.

Spawning
Shulkers spawn during generation of end cities, which are located on the outer islands of the End. They often spawn on the walls of the dungeon. Once killed, they do not respawn.

Appearance
The shell of the mob looks similar to a purpur block, blending in relatively easily to its surroundings. Inside the shell of the mob lies its "core", a small yellow head.

Behavior
Shulkers generally remain stationary, attached to an adjacent solid block. However, if the block the shulker occupies becomes something other than air or the shulker finds itself not adjacent to any solid block, it will attempt to teleport (5 attempts per tick) to an air block within a 17×17×17 cuboid centered on the shulker that is adjacent to a solid block.

Shulkers will occasionally open their shell for 1–3 seconds to peer outside. When a target comes within about 16 blocks, it will open up fully and shoot bullets which only move along the X, Y, or Z axis. The projectiles can be destroyed by attacking them. If the bullet hits an entity, it does of damage and inflicts the levitation status effect for 10 seconds. As long as the target is in range, the shulker will continue to fire every 1–5.5 seconds.

When its shell is closed, a shulker has armor points (80% damage reduction) and is completely immune to arrows. When the shell opens, it loses this natural armor and takes damage as normal. When at less than half health, a shulker has a 25% chance of teleporting (as described above) after taking damage. When a shulker is attacked, other shulkers in the area will target the attacker as well.

Shulkers are immune to lava and fire.

Trivia

 * The name shulker is short for "Shell Lurker"
 * By using commands, they can be made to be part of a team to attack other teams and can be used as defense mobs. In that case, it won't attack its teammates, but will target most hostile mobs without provocation.