Nightmare

A Nightmare is a malicious entity, a type of fiend that exist in the dimensions beyond the natural world. These creatures lurk at the borders of dreams, watching, drooling with hatred and greed.

Etymology
The word "nightmare" is derived from the Old "mare", a demon or goblin who torments others with frightening dreams. Subsequently, the prefix "night-" was added to stress the dream aspect. The word "nightmare" is cognate with the older term nachtmerrie and Nachtmahr.

Morphology
Nightmares in the physical worlds are quadrupedal monsters with a skeletal build. They have the head of a vile sickly horse, with elongated sharp teeth and two large glowing eyes on either side. It is mostly dark brown or black, except for it's legs and arms that are skinless showing muscle and veins. There is a ridge down its back with multiple spines and spikes. Instead of hands, its forearms have large, sharp, scythes. Its powerful legs lead to large Hooves. They are known to be able to run at speeds of 90 kilometres per hour almost 56 miles per hour as stated by the few people who have survived an encounter with these beasts. They are believed to be so dangerous that no man has ever fought one and lived, the only ones to have seen them are those lucky enough to escape, either by taking to the air or outrunning them on a Locevi or another kind of steed, although Nightmares can outrun a horse with relative ease.

Feeding
What little is known about Nightmares is that they enter the dreams of sleeping victims, to hunt in the dreams they hunt the sleeping person mercilessly while consistently consuming their life force, people visited by Nightmares rarely survive until dawn. They prefer to hunt children and adults who have a more powerful life force than the waning of the elderly. The victim will not awaken from the Nightmare's feeding although anyone else sleeping nearby is likely to wake up and see the Nightmare over the victim, in this case, both the witness and the victim are likely to perish.

Breeding
Nothing is known of how Nightmares breed or multiple, Rethmaryss theorizes that they are born from the life-force they consume, but there are no sources supporting his claim, and for good reason.

Communication
Nightmares never seem to appear in groups, there is always only one, it is unknown how they are able to only appear to a single person at a time.

Distribution and Habitat
Nightmares live in another dimension different from the natural world, it is a vile world where none has ever returned from.

Predators
Nightmares are believed to have no natural predators, they are said to be apex predators themselves, although if they have predators, it leaves people to speculate what kind of creature can bring down a Nightmare