Minecraft Dungeons:Ancient Guardian

The Ancient Guardian is the final boss of the Hidden Depths DLC that spawns in the Abyssal Monument. It appears similar to the Elder Guardian but is purple colored and has a pink eye. It has been corrupted by shard from the Orb of Dominance, hence it has very End-like appearance like any other main bosses.

Appearance
The Ancient Guardian is an oversized Elder Guardian with a predominantly dark purple body with lighter purple stripes on its back. All of its spikes are a light purple to white in color and its eye is a light purple in color with a white iris. On its back is a few patches of algae, coral, and seaweed, with some on its tail. Its face is full of cracks and a long scratch is seen across its purple eye.

Behavior
When the player reaches the arena, the Ancient Guardian will enter by bursting through a wall. It can swim away from the arena to avoid damage. On top of that, it has three attacks it uses every so often:

Ancient Beam
It is capable of launching a beam at the player, which behaves the same way as its weaker counterparts.

Ancient Summon
It can summon guardians whilst keeping out of the arena.

Ancient Bombs
Every so often, the guardian will come into the arena and summon a number of explosive naval blocks in the arena which explode after a given time, though it will cancel this attack after it's taken enough damage.

Ancient Wave / Spike ram
While in the arena, it will also try to attack the nearby player by piercing them with the spikes or stomping them with its body, which will make a fairly sized shockwave.

Trivia

 * At one point in a Tweet on Twitter, the developers referred to the Ancient Guardian as being the corrupted master of Guardians and Elder Guardians.
 * It has a very unique cinematic cutscene before the fight, where it's seen destroying part of the monument in order to challenge the player.
 * It is debatably the hardest boss in the game.