Nightmare (creature)

A nightmare is a neutral evil outsider from the Lower Planes. They are a type of fiend that exists in the dimensions beyond the natural world.

Physical description
Nightmares are evil creatures that appear to be large black horse with flames wreathing its hooves, flowing forth in the shape of its mane and tail, and trailing from its nostrils and red eyes. If killed, the nightmare’s flames gutter out, leaving a mane and tail of ash that quickly disperses.

Mount
Nightmares are often conjured into the world to serve as steeds for evil priests and wizards. Sometimes they are sent to a mortal as a “reward” for service to a powerful fiendish lord. A nightmare will sometimes serve a powerful evil creature as a mount. It possesses the ability to travel to other planes and a nightmare can bring its rider to one with it. A nightmare extends its resistance to fire to its rider. According to legend, particularly powerful nightmares can also carry their riders to and from the Shadowfell. There, they serve as steeds to powerful evil beings such as hags and demon princes. One should be careful to think a nightmare to be a stupid beast; they are as intelligent as a human, but also wicked and depraved.