Minecraft Dungeons:Ancient Guardian

The Ancient Guardian is the final boss of the Hidden Depths DLC. It spawns in the Abyssal Monument.

Appearance
The Ancient Guardian is an oversized Elder Guardian with a predominantly dark purple body, as well as three pink stripes. All of its spikes are a light purple to white gradient, and its eye is pink in color with a white iris. On its back are a few patches of algae, coral and seaweed, with some on its tail. In front of the algae, the orb’s shard appears to be lodged into its body. Its face is full of cracks and a long scratch is seen across its 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 that it uses every so often:

Ancient Beam
It is capable of firing 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 cannot 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 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 its spikes, or crushing them with its body, which produces a shockwave.

Trivia

 * In a Twitter post, the developers referred to the Ancient Guardian as being the “corrupted master” of the other Guardians and Elder Guardians.
 * It has a unique cinematic cutscene before the fight, where it is seen destroying a part of the monument in order to challenge the player.