Nightmares (Dungeons and Dragons)
From Multiversal Omnipedia
Nightmares are evil entities from the Lower Planes that take the form of a night-black stallion, with a skull-like face, burning red eyes, poisonous vapor rising from their nostrils, and fiery hooves and breath. They gallop in great herds across the Gray Waste, and can be summoned to service by an evil wizard in exchange for finely crafted platinum "oats."
