In the fiery illumination, the horse's jet-black mane, tail, and hooves gleam red-hot. Eyes ablaze, it charges, leaving a smoldering trail. An otherworldly whinny escapes its mouth, merging with the crackle of flames, a spectral steed surging forth in a blaze of supernatural intensity.
A nightmare appears in a cloud of roiling smoke, its mane, tail, and hooves wreathed in flame. The creature's unearthly black form moves with supernatural speed, vanishing in a cloud of brimstone as quickly as it appeared.
Dread Steed. Also called a "demon horse" or "hell horse," the nightmare serves as a steed for creatures of exceptional evil, carrying demons, devils, death knights, liches, night hags, and other vile monsters. It resembles a fiendish horse, and a nightmare's fiery red eyes betray its malevolent intelligence. A nightmare can be summoned from the Lower Planes, but unless a worthy sacrifice is offered to it as food upon its arrival, the nightmare displays no special loyalty to the creature it serves.
Creating a Nightmare. Nightmares don't appear naturally in the multiverse. They must be created from pegasi. The ritual that creates a nightmare requires the torturous removal of a pegasus's wings, driving that noble creature to evil as it is transformed by dark magic.