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.

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 enters 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
The Ancient Guardian can summon guardians to assist itself during battle. It usually summons about 3 guardians near the player, but this attack sometimes spawns an elder guardian instead. It can’t spawn anymore elder guardians if there is already one alive.

Ancient Bombs
Every so often, the guardian comes into the arena and summons a number of explosive naval blocks that explode shortly afterward, though it cancels this attack after becoming sufficiently damaged.

Ancient Wave / Spike Ram
While in the arena, it also tries to attack the nearby player by piercing them with the spikes or crushing them with its body, which produces a 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 unique cinematic cutscene before the fight, where it is seen destroying part of the monument in order to challenge the player.