Shulker

"Adventurers should explore the outer islands of the End with care - in among the blocks of purpur hang these cannily camouflaged critters. Get too close, and their block-shaped shells pop open, allowing the mollusk-like Shulker to launch a homing projectile!"

- Marsh Davies

Shulkers are box-shaped hostile mobs found in end cities. They hide in their shell to blend in with surrounding purpur blocks and guard the city's various treasures.

Spawning
Shulkers spawn during generation of end cities, which are located on the outer islands of the End. They usually spawn on the walls of the city. They don't despawn naturally, even in Peaceful difficulty, and once killed, they don't respawn.

Drops
Shulkers drop 5 experience when killed by a player or a tamed wolf. They also have a 50% chance to drop a shulker shell, plus 6.25 percentage points per level of the Looting enchantment (to a maximum of 68.75% with Looting III).

Behavior
The shell of the mob looks similar to a purpur block, blending in relatively easily to its surroundings. Inside the shell of the mob is a small yellow head with two eyes. Purple is the default color when using spawn eggs, while white is the default when using or  spawners. Spawning shulkers with other colors can be done using the command, as detailed below.

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, or the shell cannot open, 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. If it finds no solid blocks to teleport onto (like when in the Void) it will "attach" to the air and not move.

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 guided projectiles (which follow the player) which only move along the X, Y, or Z axis and leave trails of white particles. The projectiles can be destroyed by attacking them, or blocked with a shield. If the bullet hits an entity, it does of damage and inflicts the Levitation status effect for 10 seconds. (Levitation has no effect underwater, or on players in boats.) As long as the target is in range, the shulker will continue to fire every 1–5.5 seconds. If the shulker's target dies while the bullets directed at that entity still exist, they will simply fall to the ground.

When its shell is closed, a shulker has armor points and deflects 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 don't take burning damage from lava or fire, but they will still drown in lava. They will teleport when touched by water.

In Peaceful difficulty, shulkers will stay within the world. However, they will not attack.

Despite their similarities with blocks, they remain with multiple differences from them. For example, mobs will try to pathfind through them rather than walking around or jumping over them, and falling on them from a height does not produce particles. Their spawn egg will also not destroy blocks such as grass.

Shulkers can be hooked by a fishing rod. However, they cannot be reeled.

Dyeing
Shulkers can be dyed in a similar fashion to sheep. To do so, any of the 16 dyes on a shulker and the shulker will turn into the corresponding color of the dye.(Seems to be broken as of 1.14.1)

Transportation


Shulkers can be moved by boats or minecarts; they will board a boat/cart which is pushed into them. In a boat, the shulker retains the orientation it had before it was put in the boat. For example if a shulker is attached to the ceiling: it is possible to build a platform adjacent to the shulker and slide a boat under it, at which point the shulker will be moved to the boat but appear upside-down. A boat's sides block some of a shulkers projectiles (more if it is upside-down).

A shulker pushed through the exit portal will be transported to the origin in the Overworld. Since shulkers teleport when not adjacent to a solid block they must be pushed down the central pillar of the exit portal with a piston.

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

Shulker bullet
A shulker bullet is a guided projectile that is shot from shulkers, and they follow the player along the X, Y, or Z axis and leave trails of white particles.

The shulker's projectiles also have entity data which control its movement.

The bullet can be destroyed by hitting it with a sword or shooting it with an arrow.

Trivia

 * The word "shulker" is a portmanteau (combination of multiple words) of "shell lurker".
 * All shulker named 'Dinnerbone' or 'Grumm', the mob will flip upside-down, revealing a spiral pattern on the base. This appears to also lift the shulker the same height as a pressure plate.
 * Placing a gravity-affected block such as gravel or an anvil on the shulker will lift while the shulker opens its shell and after some lifts the block will drop as an item.
 * Shulkers can also begin to attack each other, in which case they will shoot fully guided bullets at each other, but will not be affected by levitation when hit. The normal teleportation habits apply during shulker vs. shulker battles.
 * One can use this to their advantage, as this would cause the shulkers to ignore the player and make them easier to take out.
 * 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.
 * Shulkers have exactly the same size as a full-sized block, but their model appears to be just a tiny bit smaller.
 * When standing on a shulker's shell, you can sneak and will not fall off, like with other blocks. If the shell is opened sideways, this can simulate a vertical slab, which you can still stand and sneak on without falling. If it closes its shell while a player or mob is on, they will fall off.
 * If given the invisibility effect, only the shulker's shell will turn invisible. This is different to most other mobs such as armoured mobs and saddled pigs, where the living part of the mob turns invisible with the outer areas remaining visible.
 * Shooting an arrow at a shulker with a closed shell, the arrow will bounce off of the shell, similarly to when arrows are fired at players in creative mode.
 * When teleporting or spawning, shulkers will reorient themselves depending on the side of the block that they are attached to. This means that shulkers may appear sideways or even upside down.
 * Shulker spawned with will appear to have a white shell instead of a purple shell.
 * In the game's texture files, the shulker bullet is named "spark.png".
 * Shulkers teleport should a falling block such as sand falls on them. If spawned in with no AI and sand is dropped on them, they will darken in color and the block will constantly hop. If with AI and sand is dropped on them and the shulker has nowhere to go, they will suffocate.