wraith

Monster Manual:

“THIS RESTLESS APPARITION LURKS IN THE SHADOWS, thirsting for souls. Those it slays become free-willed wraiths as hateful as their creator.

Wraith Tactics

A wraith uses hit-and-run tactics and flanking to gain combat advantage, phasing through walls, doors, and other obstacles to break line of sight. When bloodied, the wraith flees, only to return after it has regenerated most or all of its damage.”

wraith

Adventures in the Thunderpeaks Mundungus