Nightmare (creature)

Nightmares, sometimes called hell horses or demon horses,  were fiendish equines named after the terrible dreams suffered by those that encountered them. They were wicked creatures best known for serving as mounts under a variety of malevolent beings throughout the Lower planes.

Description
Nightmares were seemingly emaciated stallions, approximately tall at the shoulders, with night black coats. On further examination however, their warhorse-like exterior was revealed to be entirely superficial. They had huge heads, fangs like vipers, malevolent dark eyes often illuminated by red hot flames and spouted orange fires when their nostrils flared. Wreathed in fire, their manes were wild and their tails unkempt, but turned to cinders and quickly dispersed upon death.

Their steely hooves left scorch marks wherever they went but the tracks left mysterious patterns and gaps. They galloped through the night with unnatural agility, their black bodies blending into the darkness leaving onlookers with only the sight of racing, infernal flames that appeared and disappeared in smokescreens of brimstone. Rumors had it that the creatures moved so fast that they could only be seen as a blur, but those that had viewed them speculated that they could move between shadows or teleport, which would explain their ability to stop and start in an instant and suddenly appear without seeming to have moved.

Personality
Nightmares were callous and cruel creatures that stalked reality searching for those it could victimize. They displayed hatred towards all life of the Material Plane and exhibited an infernal intelligence unseen in true beasts. Rather than simply murder their targets, they used their supernatural powers to strike terror in them first, making them fear for their lives and killing them once they were reduced to panicking wrecks. One of their favorite tricks was to allow their victims one last moment of feeling safe before suddenly reappearing, dashing their last remaining hope and then striking the killing blow.

Despite being wild and roaming creatures they were known to serve willingly as mounts during missions of malice, but only for those of sufficient wickedness and ability. Those that wished to ride them would be wise to remember that nightmares were not simple steeds but fiercely independent and untamable fiends with their own instincts and agendas. Prideful and egotistical, nightmares often acted upon their own wills even if such actions ran counter to their goals of their supposed masters and sometimes even at their expense. Even if both parties desired to commit evil deeds their exact methodologies could be incompatible and attempts to force them into servitude often ended poorly. Only after forging a bond with them over time would a nightmare become loyal to a rider and only then would the two become true partners in villainy.

Abilities
The titular power of nightmares was their ability to appear in dreams, either before the victim had encountered them in the flesh in a kind of ill omen or in the minds of survivors after a terrifying attack. They could shift to the astral and ethereal planes, as well as the Shadowfell, at will, and despite their lack of wings could magically fly even faster than they ran. Their hooves typically ignited flammable objects and they could leave massive walls of fire in their wake.

Nightmares were often surrounded by a haze of smoke thick enough to prevent others from seeing them but that they could see through perfectly. They often exhaled a searing, sulfurous smoke in the midst of combat, neighing in fits of rage while snorting out the noxious gas. The blinding, choking cloud left enemies caught within it wheezing and unable to properly fight back against the nightmare.

Combat
With tooth and hoof, nightmares savaged most creatures they came across. Beings from the lower planes were typically spared from their fury but other entities weren't so lucky, particularly those from the Material Plane. They utilized hit-and-run tactics, targeting separated members of groups and blocking off means of escape through fires, speed and their ability to move between planes. Only skilled riders could properly fight with a nightmare while riding on top of it.

Society
Nightmares of the Shadowfell were unique in their tendency to hunt in small, predatory herds similar to wolf packs. They haunted untraveled roads, either in the Shadowfell or Material Plane, looking for the rare, night-going wanderers to prey upon. Passages known as "ember ways", so called due to the smoking hoofprints left behind in the wake of their makers, were regarded as dangerous paths even by the denizens of the Shadowfell and even during the day.

The bleak realms of the Gray Wastes and the Shadowfell were most closely linked to nightmares, but they could be found and shaped by other planes; the Abyss for example having mutated its nightmare inhabitants into demonic variants. Such nightmares were usually lone wanderers that murdered individual targets and smaller groups, but those with herds shared tighter bonds and possessed unique social structures not found elsewhere. Sin's Reward, a nightmare barded in spiked, black armor and cloaked in black smoke and white flames, was the master of all nightmares in the Nine Hells. Meanwhile the mares of the Abyss were commanded by the mutant mare Thunder of Hooves, a massive, six-legged nightmare that ruled through violence and intimidation. The two mated annually in the Shadowfell despite their mutual hatred of one another, producing three powerful foals, two of which would go to one of the parent's planes and one of which would stay in the Shadowfell.

On rare occasions, somewhere between a year and a decade, a sinister night came for all beings of evil known as the Gloom Meet. The denizens of the Lower Planes, as well as the Shadowfell, met together in the Glooms of Hades to conduct dark diplomacy. The wicked participants gathered in an unholy meeting to settle their differences, create new alliances and discuss their future agendas. Two weeks before the Gloom Meet began, nightmares heralded its coming, racing across the planes and becoming more noticeable throughout the multiverse, particularly in the Gray Wates. In the final moments before the Meet, nightmares charged in a terrifying stampede towards its final destination leaving a trail of hoofprint-shaped scorch marks behind them. It was by following such marks that a few planar scholars and adventurers found the Gloom Meet's location themselves, allowing infrequent accounts of such meetings to exist.

As Mounts
Nightmares were often conjured into the world to serve as steeds for evil priests and wizards. Sometimes they were sent to a mortal as a "reward" for service to a powerful fiendish lord. A nightmare would sometimes serve a powerful evil creature as a mount. It possessed the ability to travel to other planes and a nightmare could bring its rider to one as well. A nightmare extended its resistance to fire to its rider. According to legend, particularly powerful nightmares could also carry their riders to and from the Shadowfell. There, they served as steeds to powerful evil beings such as hags and demon princes.

Creation
Nightmares did not appear naturally. They were the result of a dark magic ritual applied to pegasi. The ritual involved the removal of a pegasus's wings by torture, followed by its transformation and abandonment of its noble qualities in favor of evil.