Nightmare

Nightmare is a female horse demon-ghost who wanders the dream realm.

Legend
The Nightmare is summoned when one is in a bad dream, by bloodletting, and chanting her name three times. After those three times, the Nightmare rides down into the dream, and escorts someone out of the dangerous part of their dream, and eventually out of the dream.

However, for each summon, the Nightmare exacts a toll. The Nightmare eats one day's worth of dreams the first summon, then one week's worth of dreams the next summon, and then on the third summon, turns someone into a Wight - a ghost who causes bad dreams.

As soon as the wight makes more bad dreams, someone is encourages to summon the Nightmare.

Typically someone will find a book in their dream that instructs how one can summon the Nightmare.

Abilities
Wight Creation: The Nightmare slowly absorbs a rider into her body, to make a centaur sort of creature, while the flesh slowly strips from the rider's body.

Generation of Wings and Horn: The Nightmare can create a set of wings, and a horn.

Sleepiness: Nightmare can expel noxious air which forces someone to fall asleep within a matter of seconds.

Dream Override: The Nightmare can manipulate others' dreams better than they can.

Interplanar Traveling: The Nightmare can travel from the material plane to the dream plane at free will.

Dream Consumption: The Nightmare can consume dreams, and seems to feed on dreams as a primary way to survive.

Overall, the Nightmare is cunning and charismatic. However, due to being an undead being, the Nightmare is highly insensitive, therefore some riders find her unresponsive. There is no saddle during the ride, and instead someone usually has to just grab her mane, and go.

After dismount, a rider is usually considered done.

Role In N:Era
In N:Era, when wandering the graveyard, Clovur and Portus find a book which mentions the Nightmare. The two use the book, and the knowledge within to scam others, not truly caring about the summoning of the horse and how that affects others.

As dozens summon the Nightmare, Ahmond tells Cyras about the eventual problem, and how they'll all be reaped of sleep, and turned into Wights.

Cyras instructs everyone to summon the Nightmare at once, with Rosod keeping a bell. By sounding the bell, she'll put them into a lucid dream. As the Nightmare keeps trying to go to one dream, a new summon happens, and a summon afterwards, until Rosod rings the bell again, forcibly waking everyone up.

As Nightmare appears in the material world, and attempts to exact the toll, Cyras says that technically Rosod woke everyone up from the bad dream, and thus Nightmare deserves no payment. The members of Team N:Era also wrangle down the horse, long enough for Owlis to safely arrest her.

Nightmare's punishment is unknown so far.

Trivia

 * Nightmare is likely the strongest N:Era one-shot villain, only being beaten ultimately by dozens of people working together.
 * Nightmare's the only character to have been spanked for non-punishment reasons.
 * Nightmare can speak both Draconic and Demonic, along with Undead.
 * Nightmare is the only demon character introduced so far, as Lilith is an Aetherperson despite being Queen of the Devils.
 * Since all demons serve a devil master, this means Nightmare has a master who has yet to appear.