Abyss

"Such a wickedness as I felt in that dark place is unrivaled. Never has my soul been so shaken to be in such a presence, not in any pit of Thogros nor the conjoined worlds I have wrought between them."

-Hafthure, after traveling to the Abyss during his banishment of Ashima's children.

A parallel universe represented by a massive chasm, illuminated by fiery light except the top and bottom, which respectively ascend and descend into darkness. The Demon Queen has said that there is a top of the Abyss, yet no surface.

History
After the Fracture, the main universe was created. Within it was contained a multitude of alternate universes and pocket realms, each carrying out different variations of the same story as they exponentially multiplied to handle every possible scenario, all stemming from the same origin. However, The Other took notice at this cosmic inception that there were other universes completely separate from this one. One of those was The Zone, and another was the Abyss.

Ashima's adulterous affair with Krulem resulted in her giving birth to a multitude of cruel, powerful creatures. To expel this abominations from the universe he labored on, Hafthure constructed an alternate universe and removed Ashima's brood to it. Originally, he crafted this universe connected to the human universe as well as the Abyss. However, upon observing the malevolent nature of the denizens of the Abyss, Hafthure felt the need for another layer of protection between this universe and his. Thus, the creation of the gateway universe was actually meant as another barrier between our world and the Abyss, not just for the Thrakr demon universe as it has been assumed for so long. This shows how much Hafthure, one of the more powerful Old Beings, was shaken by his encounter with the Abyss.

Due to the nature of Hafthure's construction, it became technically possible, however improbable, for beings to cross from Thogros, through Formin, through the demon universe, into the Abyss and vice versa. It would be nearly impossible for anyone to cross all four dimensions, therefore when crossings did occur, it was usually between one neighboring universe. This is how the Demon King and his mate managed to cross from the Abyss into the demon universe. The Demon King had been on par with his contemporaries in the Abyss, but found himself now greater than many of the Manas Nui, and thus established himself as a ruler among the demons.

Throughout history, demon incursions were extremely rare and occasionally would result in planetary extinction if they occurred early enough in the evolution of that planet's biosphere. The Ancients themselves have no records of any demon invasions, although it is doubtless some occurred. In a fascinating development, the record of Doctor Allison Shaw's interaction with the Inferrectus contained several references to an event in the history of the Elder Race where they faced an enemy similar in description to demons. This implies crossings occurred in other galaxies as well, although with the demon universe and not necessarily the Abyss. The Ancients' interrogation of the Former Artificial Intelligence may have implied some demonic encounter, but the transcript is scrubbed shortly after this mention.

In Universe A, during a second demonic invasion led by the Demon King, the cybernetic soldier Darren became a consort of the Demon Queen, and subsequently was shown a route from subterranean chambers of the demon universe into the walls of the Abyss. Darren later taught this path to Jackson, who used it to escape home through the Temple of the Grotesque. Darren was struck with shards of Blade's sword, which he absorbed using the gift the Demon Queen had given him. This granted him the power of any essence he absorbed, and he proceeded to kill the Demon King and forge a truce with humanity, forbidding any further incursion. Darren may have possibly grown so powerful that he was able to extend this warning into subsequent timelines. All we know is crossings from that universe to Earth ceased entirely, but occasional crossings from the Abyss were known to occur.

Inhabitants
Many of the Cults in Formin around the time of Norman Phillips were inspired by creatures from the Abyss. These beings were powerful entities who made their homes in the crags on the walls of the Abyss. They never strayed too far towards the surface, or too far to the depths, lest they fall into the web of the evil that lies at the bottom.

The Grotesque - A humanoid being who dwells within a massive, lucid stone temple built into the walls of the Abyss. This is one of the only recognizable locations of the Abyss, and it's only constructed feature. The Grotesque conceals his visage with a smiling white porcelain mask, a even more nightmarish face with dark eyes, tear trails and a twisted smile. The Temple of the Grotesque serves as the only known path from the Abyss into other realms. Most famously, Jackson and the consorts of the Demon Queen used this pathway to escape back to Thogros. Those who enter the Temple are faced with labyrinthian stone halls, and a series of challenges set forth by the Grotesque while he stalks and hunts them. The Grotesque is known to act in spite of the Fiend of the Abyss, as the two have some ancient animosity.

Tempest - A beast of storm and destruction who inhabits the Abyss. A handful of crossings to Formin inspired the creation of Tempest Warlocks, a band of magicians who possessed the Tempest Stone, supposedly created by the Tempest itself. Many future iterations of their belief system linked the Tempest's presence with storms, suggesting the original Tempest's true form was hidden within a tornado or some other kind of storm. The Tempest wanders the upper portion of the Abyss, and is among the less subtle inhabitants, as its approach can be heard from quite a ways away. True to its name, the Tempest generates thunder and winds where it goes, and thus quite a lot of noise.

Sickly Child - The origins of the Sickly Child are unknown, however there have been many theories that speculate he is not a native of the Abyss, and rather represents the living corpse of a deceased infant. Gerald Rowan was known to be dismissive of these rumors, but unable to disprove them. The Sickly Child manifests as a diseased male human child, who appears to be suffering from famine and disease. His appearance is generally considered a bad omen, and he appears as a minor figure in the pantheons of many cults including Crimonyst, Opjomp, Black Riders and Tempest Warlocks. The sisterhood of the Dark Goat is the only organization native to Thogros known to acknowledge the existence of the Sickly Child in their rituals.

Fiend of the Abyss - a hideous, bulbous, gigantic monstrosity native to the Abyss. The Fiend possesses little intelligence, and operates as a feral beast that clings to the walls of the Abyss and hunts for anything weaker than itself. The body of the Fiend is a corpulent mass of swollen pink flesh, criss-crossed with open wounds that ooze viscous, clotted blood from the constant abrasions of it's fat rolls against one another. While the Fiend resembles at first a bloated worm or slug, the multitude of long, powerful arms ensure it is quick moving predator with a strong grasp. The Fiend is powerful enough even to launch itself from one end of the Abyss to the other, swinging on outcroppings of rock like a multi-limbed simian.

It - surely the most powerful of the creatures that dwell in the Abyss. It occupies the deepest portion of the ravine, spinning away at a hidden web and waiting for prey to torture. IT possesses the ability to travel between worlds at will, and will travel across planes during times of express stress and disorder. During the War of the Duck, It roamed freely, untethered due to the chaos taking place. It crosses into our world more often than many know, but is immaterial in our world and so thus must take the form of objects that already exist. This does not stop it from exerting it's malign influence upon innocents in times of chaos. During childhood, the spawn of Tkarmen had an encounter with It, however he was spared for an unknown reason.