Skeleton
From Dungeon Defenders 2 Wiki
Summoned Enemy
Skeletons are a type of monster summoned by the Dark Mage monster. Specifically, they come from the corpses of fallen enemies that haven't dissipated. These skeletons generally come in 2 different types: The smaller, human-like skeletons, and the larger, Orc-like ones. They can also spawn in some lanes on certain maps.
Skeletons are dangerous because they spawn where they previously died, giving them a head-start walking towards defenses and distracting your defenses from more important enemies like Javelin Throwers and Witch Doctors. They overwhelm defenses very quickly, but AoE Sources of damage can hold them off.