The mooshroom monstrosity appears to be the remnants of an ancient redstone monstrosity somehow reactivated by mushroom spores. It is a golem made of stone and redstone patches, as well as mushroom spores sprouting out of it's body. The mushrooms are the same as the "Red Mushroom" from the original Minecraft game. It appears to have multiple cracks within the body and red outlines within its torso. It has two black eyes and a third empty eye socket on its forehead, and a red jaw. It is about 5.4 blocks tall.

More info: https://minecraft.fandom.com/wiki/Minecraft_Dungeons:Mooshroom_Monstrosity

The size was doubled by 23% more than previously published. The only thing that has changed is the size of the pieces. 11 papers.