Nightmare

So, the Nightmare. The Bestiary doesn't provide much info on what exactly it is beyond listing it as both a fiend and a beast in addition to saying that it might be used as a steed for evil creatures. It boasts some interesting abilities, like exhaling poisonous smoke and being able to plane shift along with its rider. Even then, I find it a little underwhelming—so let's go on a little bit of a deep dive.

The word itself is a combination of "night" and the Old English "mære," the latter meaning incubus. Its variations appear in other languages, like Swedish, Old Norse, Danish, Norwegian, and even Polish ("mara" meaning a hallucination or a haunting dream,—here's your fun fact of the day). We all are aware of what a nightmare is. A bad, bad dream. It is kind of ironic then that the creature named after it has nothing to do with dreams.

Am I trying to convince you to attack your party in their sleep with a flaming horse? Yes. No, all I'm saying is that you can make the monster a little more interesting.

- Max

Hook 1 (Max) - A Mare So Very Fair

"That horse is evil, I tell you." Both servants look to the black steed that was gifted to their liege by a mysterious woman not so long ago. The animal bears its teeth and glares at them with obvious and uncontained hatred. "Fastest beast I've ever seen, true, but there's something wrong with it, I swear by my mother's grave." The older of the two men spits. "Makes me sick just being near it."

"I hear it killed old man Tanner" the boy exclaims. "Kicked him square in the face it did." A shiver runs down his spine. "Wish the lord would be rid of it, to be honest." The horse lets out a fume through its nostrils as if it can understand.

"Doubt it'll happen, lad." The old man sighs a heavy sigh and takes up his tools. "Well, best get it over with. Keep it still, will you?"

Hook 2 (TJ) - Dreamrider

The past three nights, Hinli dreamt. This was not unusual. She imagined that most nights she dreamt, but somewhere in the bliss of sleep she didn't remember the dreams when she woke up. These dreams, however, she remembered—at least pieces of them. What she did remember of them was not pleasant. Primarily, her recollection of these dreams consisted of one major feature: the thundering of hooves right before she woke up. There was one unmistakable and unsettling fact about these cacophonous hoofbeats. Every night, they got louder.

Hook 3 (Reece) - Cult of the Dreaded Steed

"It galloped through the streets, features alight! The fires! The blood! What wondrous destruction it showed me! I will breathe in the smoke of its essence and await! Behold! The Midnight Steed! The Bringer of Fires! You may delight in his majesty and revere his presence! BE BLESSED BY HIS DREADED RIDE! TASTE OF THE LICKING FLAME AND STAY FAST FOR THE END IS NIGH."

- Collected from the ravings of a beggar two nights before the last sighting. I worry this cult you speak of is gaining more attention than we originally thought.