Hey speaking of which, it's time I finally got around to that Abyss write-up!
The Abyss: Graveyard of Broken Realities
Some say the Abyss is a hole between the Supernal and the rest of the universe. They are misguided-the Abyss is not a "hole", as that would imply a lack of substance. The Abyss encompasses all that is unreal, including impossible substance.
Some say the Abyss is a result of Atlantean hubris, believing they could order the Supernal to their ideals. They are wrong-while the fall of Atlantis was caused, at least in part, one of the greatest Intrusions on record, the Abyss was long before Atlantis, and as a whole did not even notice it was gone.
Orkus says the Abyss is a result of his manipulations, another tool in his quest to conquer and then destroy the universe. He is lying-though like all good lies, it contains an element of truth.
In all truth, while Orkus did open the first known portal there with a working of the darkest magic and the most obscene science, the Abyss is, and always has been, a byproduct of the existence of the cosmos-in all its iterations. Quite simply, the Light is not a perfect entity, and during the rebirth of the cosmos after the Dark devours it, its creative energy is unfocused, random. It takes the form of every potential thing and every potential non-thing that can exist in the reborn cosmos, and invariably, a few manifestations of its power are...broken. Paradoxical. Simply impossible. That Which Should Not Be.
As the new multiverse cools and hardens, these manifestations of a warped potential are squirreled away in a bizarre pesudo-space that exists outside the entire cosmos-even the Annhilation Zone. This, not the hole between the Supernal and everything else, is the true Abyss-a prison and junkyard for the Failures of God, a place where the Paradox Laws may exist without harming the rest of reality.
And they are not happy about it.
The Paradox Laws, you see, are not dead, still things. They, much like physical laws in the true cosmos, proceed to enforce themselves on the formless substance of the Abyss, forming entire, stillborn dimensions around themselves. These dimensions, the Greater Abyssal Entities, have an emergent intelligence born from the interaction of their horrid inhabitants and warped internal logic, and each one is acutely aware of the fact that it is a way the cosmos could have been, but wasn't. This knowledge, that they are unwanted by existence, angers and upsets them, and so they, in their vast, alien manner, look upon the real universe with envy and hate, desiring to be the real universe, or at least destroy it so that they too may be recycled by the Light and so end their pain.
And they would have remained out there, if Orkus has not made what he considers (privately) to be one of his few blunders, and letting them in.
See, the Abyss, as a whole, requires permission; part of the genius of imprisoning the Things That Should Not Be in the Abyss is that the space is literally conceptual-if the inhabitants of the cosmos do not allow the Abyss to Intrude, in most cases it cannot. A young Orkus, unfortunately, realized this, and in his pride, thought he could use the Abyss' desire to replace reality for his own benefit. The destruction of several Anti-Gods and at least one True Entropic Master informed him otherwise. The Greater Abyssal Entities cannot be ruled, in much the same way the nuclear forces, gravity, and electromagnetism cannot be ruled-only have relatively infinitesimal bits of themselves directed towards a certain task. They can, however, be served, and as the inhabitants who thought on a more mortal scale realized, there was no shortage of people who thought as if reality itself had turned against them, and were willing to listen to the idea of...changing it.
So were born not only the first Scelesti, the Magi of the Abyss, but also the innumerable cultists who serve, knowingly or not, the Things That Should Not Be. And as they have established footholds, the Abyss has found it easier and easier to Intrude, almost to the point where they don't even need to ask, even subconsciously.
Terminology: A Greater Abyssal Entity is, as mentioned, a broken, semi-sapient universe born from a Paradox Law, a physical, mystical, scientific, or biological natural law of the universe that simply doesn't make sense and would cause damage to the fabric of the universe. When allowed into the Tellurian through dark deeds, morbid desires or evil ritual, the resultant Abyss-born phenomenon is called an Intrusion. These are not always living or even physical entities, and in fact often manifest as a twisting of natural law into the bizarre; distortions of the space-time continuum are a good example, though far from the only. Which isn't to say they don't happen of course-in this case the entity is called a Gulmoth, and usually only stays in the Tellurian long enough to accomplish some arcane goal that furthers the agenda of the Greater Abyssal Entity that spawned it, sets the stage for more Intrusions, or the destruction of reality (though this isn't necessarily large-could be it just wants to devour a single soul or some relatively small thing that creates a lot of pain and heartache for a smallish number of people). In particularly large-scale or catastrophic Intrusions, the Gulmoth may become stuck in the Tellurian and become an Acamoth, an emissary of the Abyss. The Acamoth invariably become quite powerful as they parasitically leech off of the Tellurian's energy and gain the ability to send dreams that entice people to provoke Intrusions, form cults of it, or even to give the Acamoth permission to use an individual's mind as a "home away from home", using it as a gateway for Abyssal energies to stream through and return the Acamoth, however briefly, to the Abyss. Needless to say, this is not good for a person's sanity or moral compass, so an Abyssal sojourn by an Acamoth is phrased as an archetypal Devil's Deal-"allow me to stomp around your subconscious for a bit, and I'll give you special powers". Naturally, these Investitures come built with an expiration date, so that the Acamoth get repeat customers.
(I'll probably return to this once The Left-Handed Path for Mage comes out, and I can explore the Scelesti from their POV)