The Nightmare
If the Dream is a realm of beauty and tranquility, then The Nightmare is the polar opposite of it - a realm of horrific visions and madness. As its name suggests, it is the place where eldritch nightmares come from to torment mortal minds through their dreams, sending horrible monsters to attack their psyche.
The Nightmare is described as an infectious disease that originates from a horrific creature known as Z'thulun, the Dark Father, from who's flesh and blood an army of monsters rise up to spread his influence across the Dream. From his Dark Citadel, Z'thulun continues to lead his nightmares to attack both the Dream as well as the mortal realm, his twisted tentacles and infinite eyes desiring nothing more than to send the world to havoc and chaos. Their true end goal is to gain control over all of the Afterworld.
There are those in Auria that have fallen under the Nightmare's grasp to worship Z'thulun as the one true god, spreading his influence through heretical rituals. These mortals have created a cult known as the Calamity's Edge.
When any lifeform falls asleep, their soul travels into the Dream to rest and enjoy otherworldly sights... but there can be times when they reach the Nightmare instead or at least part of it, leading to troubled sleep full of fearful sights and horrendous visions that may only drain the person's energy instead of the opposite. People all over Auria have wondered about the nature of the Dream as well as the Nightmare and how they truly function and many questions have been raised towards the Dryads who continue to shrug their worries away to keep the Nightmare's true identity a mystery to them, simply playing them off as a little worry the Dryads can handle.