Nightmares, the evil steeds of the Lower Planes, serve as mounts for baatezu, tanar’ri, night hags, and powerful undead lords. They look like large, powerful horses with a jet black coat. Nightmares have glowing red eyes, flaming orange nostrils, and hooves that burn like embers. Their long manes and tails are ragged and wild. They understand commands from evil riders and communicate among themselves by empathy.

Combat: Nightmares hate all life. They often attack any non-lower-planar creature they encounter (and sometimes lower planar creatures, too). Their fangs inflict 2d4 damage, their two burning front hooves each inflict 2d4+2 damage and ignite combustibles.

During combat, excitement causes the nightmare to emit a hot cloud of noxious vapors that blinds and chokes all within 10’. Victims must save vs. paralyzation or take a -2 penalty on their attack and damage rolls.

Although they have no wings, nightmares can magically propel themselves through the air at an impressive rate. They fly through the Astral and Ethereal Planes at will.

Habitat/Society: Nightmares serve many lower-planar creatures. They are intelligent and cannot be treated as casually as a horse. They willingly serve as mount for any mission involving evil. However, for the unwary rider a nightmare’s own ambitions can prove insurmountable. These hateful steeds often do what they want rather than follow the wishes of their “master”. A nightmare poses the same problems as magical weapons with large egos.

Any non-native on the Lower Planes can attract the attention of a nightmare to secure it as a mount. The process, which involves several spells as well as an offering for the creature’s service, requires a mage or specialist wizard of at least 5th level. The following spells must all be cast by the same spellcaster: mount (to attract the nightmare’s attention); monster summoning III (to bind it to service); and wall of fog. The nightmare comes galloping through the fog, nostrils flaring and eyes gleaming. Lastly, the master must make the steed an offering: oat-like flakes made from platinum (200 gp value). Whoever feeds the oats to the nightmare becomes its master for 72 hours.

Creatures of the Lower Planes do not perform these steps to summon a nightmare. No mortal sage knows what dark agreement they make for a nightmare’s service.

Once per year on the plane of the Gray Waste, its denizens meet in a dark and sinister Gloom meet to debate how to spread their will for the next year. Nightmares announce the Gloom meet. For two weeks before the Meet, nightmare frequency changes from very rare to uncommon. Immediately before the meeting, the nightmares herald it by riding the planes in a terrifying charge.

Ecology: Nightmares have no biological link to true horses. A nightmare is a minion of evil, without need of food or air. Nightmares are listed as carnivores because they eat fallen foes. However, nothing indicates that the nightmares derive sustenance from this; more likely, they gain their strength through service to evil.

It is said that when nightmares die of “natural causes” – if indeed anything that happens to such creatures of evil can be called “natural” – they go to the Hill of Bone in the Gray Wastes to die. There, among the bones of their ancestors’ ancestors, they lie down to die. Some of the great stallions have arranged for honor guards to pick up their bodies – even if on other planes. The wizard Nephrosis Curwen claimed to have visited the Hill of Bone:

“I had seen the hill from afar – the only white area in the Gray Wastes. I flew my broom to it, and was immediately struck hy the relative quiet of the place, as opposed to the incessant cries of the Hordlings. The Hill was very tall, and at first I took the skeletons to be those of horses. From time to time I heard a neigh or snort, and thought that perhaps there were horses nearby. Then I realized that it was the skulls themselves making the noise. Some vitality, some evil force remained in them.

“While examining the skeletons, I was surprised by a wall of fog forming near the base of the hill scarce sixty feet from me. I recognized the sound of a nightmare’s hooves, for often I had summoned such steeds in a similar manner.

“I hid myself behind a large pile of legbones to observe the phenomenon. A very ancient stallion came through the fog. His back was bowed, and silvery hair marked his otherwise ehon coat. He came at a canter, as opposed to the great gallop in which they normally appear. He neighed once very loudly, and every skull on the Hill of Bone answered him in a deafening call. Then he lay down and died, almost instantly.

“I assumed it would not be wise to remain here, and continued my quest.”