Skeletal Hellknight Bonesinger

Some undead Hellknights can command the bones of both their own bodies and others, and they primarily use this ability to temporarily strengthen themselves and summon waves of reinforcements. While just as undead as their compatriots, these so-called bonesingers have enough intelligence to join their living counterparts, though they're generally shunned and disavowed.

The bodies of Hellknights occasionally rise to continue their fight. This is just one example of an undead soldier of Hell.