Harpion Death Knight

From Introduction:

Some say these undead warriors once served the Monster King, Mortegaunt, but now in death they serve the Bone Goddess. Just look at them! If you ever have the misfortune to see one in person, the blue fire that surrounds them is a dead giveaway (no pun intended). But others say these winged mummies serve
another monarch, Thanatobassilus the Death King, and were a gift from the gods of the harpies. In exchange for favours given, they turned over the souls of their own dead servants. The Harpion death knights do not speak—at least not to the living — and so cannot answer any questions those sages have, but all agree: they are the vanguard of an undead army, and always presage an infestation of the living dead.