Elder Guardian

"... You won’t be able to snaffle up the monument’s resources even then - lurking Elder Guardians will cast Mining Fatigue on you, leaving you unable to heave your pickaxe effectively. You’ll have to seek them in the labyrinth and eliminate them one by one to be free of its effects. Alternatively, milk is a useful antidote - just make sure you pack a few buckets of the stuff!"

- Marsh Davies

The elder guardian is a hostile mob (boss mob in Bedrock Edition) that only spawns underwater in ocean monuments. It is a stronger variant of the guardian.

Spawning
Three elder guardians spawn naturally during the generation of each ocean monument: one in the top room of the monument and the other two in each wing section of the monument. They will not respawn after their initial spawn, thus there are a limited number of them per world. Elder guardians spawned with monuments do not naturally despawn, although they will be removed along with other hostile mobs in peaceful difficulty.

Drops
Elder guardians drop:

Common drops

 * 0-2 s. Looting increases the maximum prismarine shard drop by one per level.
 * 50% chance of dropping a ( if killed by fire).
 * 33% chance of dropping instead.
 * 17% chance of dropping neither.
 * The drops are affected by the Looting enchantment.
 * 1 if killed by the player.

Rare drops
The elder guardian has also a 2.5 chance of dropping a random fish as an extra drop in addition to the normal fish drop.

The elder guardian's extra drop chances
The chances is like fishing (60% chance for raw fish, 25% chance for raw salmon, 13% chance for pufferfish, and 2% chance for clownfish)

Experience
They drop 10 experience when killed by a player or tamed wolf.

Behavior
Elder guardians do not swim around as much as normal guardians, but otherwise act the same as regular guardians both in water and on land. Elder guardians will NOT swim away when approached by a player it is targeting, unlike regular guardians. Like normal guardians, elder guardians will attempt to attack both the player and squid.

The elder guardian's eye follows and stares at any nearby players, and always looks directly at its target. The eye still follows and attacks a completely unarmored player under the effects of a potion of invisibility. It seems that their eyes are coded to simply track to closest player, as they also follow players in spectator mode.

The elder guardian has three methods of attack, including firing its laser, inflicting mining fatigue, and a defensive thorn-like attack.

Laser
The laser takes several seconds to charge, doing no damage and allowing the player to move away in the meantime, and changing from purple to bright yellow. Once charged, the beam abruptly ends and deals damage on normal difficulty. The elder guardian will swim around for a few seconds before firing again. The beam cannot be dodged, and has a maximum range of approximately 14 blocks. Once the player is out of range, or if the beam is obstructed by solid blocks, the guardian's beam will disengage from the player, and deal no damage.

Inflicting Mining Fatigue
"During the development of the ocean monument I had a problem. I wanted the pyramid to feel like a maze, so you have to figure it out to get the treasure, but the bad - and good! - thing about Minecraft is that you can just rebuild everything. So the solution would always be just to knock your way through. And I didn’t want to make the pyramid indestructible because that’s also not fun in Minecraft. So after a couple of ideas we decided to have a boss guardian that would have a spell effect that would slow everything down."

- Jens Bergensten

Once each minute, the elder guardian will search for players in a 50-block radius who are not afflicted with Mining Fatigue III for a minute or longer. The players found will be inflicted with mining fatigue III for 5 minutes, and a ghostly image of the elder guardian will appear to the player, accompanied with a ghastly noise. This attack can target players through blocks, even when there is no path to that player (e.g., players who are underground), and target unarmored players under the effects of a potion of Invisibility. The image of the elder guardian is a particle effect that can be recreated by issuing the command.

Thorn like attack
Elder guardians deal of damage every time it is hit when its spikes are extended. If cornered, the elder guardian will usually extend its spikes and fire at the player, even at point blank range.

Data values
Elder guardians have entity data associated with them that contain various properties of the mob. Their entity ID is.

Trivia

 * The elder guardian's eye is actually the "head" part of the mob's model, giving the illusion of a dynamic eye.
 * The elder guardian texture has the name "jeb" on it.
 * According to Jeb, elder guardians were introduced to encourage players to solve the temple maze rather than dig through it easily. He acknowledges there are ways around it, but, nevertheless, players still have to solve the challenge in a different way.
 * Also according to Jeb, the "jump scare" by elder guardian is unintentional, instead he added it to provide a visual cue as to why players get slowed down by mining fatigue.