Minecraft Dungeons:Ancient Guardian

The Corrupted Master is presumably the final boss of the Hidden Depths DLC. It appears similar to the Elder Guardian but is purple colored and has a pink eye. It was most likely an Elder Guardian that was corrupted by a shard from the Orb of Dominance, hence its very End-like appearance.

Appearance
The Corrupted Master 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 and seaweed, with some on its tail. Its face is full of cracks and a long scratch is seen across its purple eye.

Trivia

 * The placeholder name of the Corrupted Master comes from an official post from the Minecraft Dungeons Twitter Account.
 * This boss mob is referred to as an "Ancient Guardian" in its boss music track.