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. After taking notable damage, it can swim away from the arena to avoid damage for a bit. On top of that, it has four attacks that it uses every so often:

It is capable of firing a yellow beam at the player, which behaves the same way as its weaker counterparts. A trick to avoid these is to hide behind the blocks, and then the beam won't hit you.
 * Ancient beam


 * 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. If the player has a Love Medallion, you can use it on the Guardians to help fight by your side.

Every so often, the ancient guardian comes into the arena and summons a number of guardian-shaped blocks that explode shortly afterward, though it cancels this attack after becoming sufficiently damaged.
 * Ancient bombs

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.
 * Ancient wave / spike ram

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.