Eldritch Earth: Five Hacks Deep

Looking somewhat like the demons or human art, Dreaded Man-bats have human-like torsos and legs, but large bat-like wings, and an ugly bat-like head with two small horns. Created by Atlantean sorcerers as a tribute to their demonic masters, they still fly about causing death and suffering. They famously can become invisible simply by finding a spot of shadow or near-darkness and not moving.