https://minecraft.fandom.com/wiki/Minecraft_Dungeons:Mossy_Skeleton

Appearance A mossy skeleton is a mossy variant of the normal skeleton with vines and moss covering the entirety of its body. Small patches of moss can be found surrounding its head, and vines entangled around its ribcage, it has smaller moss patches on its legs and arms. It also emits a green cloud of poison that emanates from its ribcage. This poison can affect the hero from the arrows it shoots, which inflicts a poisoned effect upon direct hit.