The Abyssal Situation
The Abyss is a chaotic evil plane in the Outer Sphere. It is accessible through huge rents in the Maelstrom, opening into fiendish depths vast beyond imagining. Sporadically, the demonic occupants of the Abyss will pour from these rents to menace one plane or another, and sometimes even tear their way into the Material Plane.
The Abyss is possessed of many layers, strung together by the river Styx. Many of these planes are ruled by powerful and unique demon lords. These Abyssal realms are pockets in which the fabric of the Abyss has slowed its relentless, changing insanity to a near-reality pace. These places are often ruled by a demon lord, either thanks to the lord’s own power over the area, or simply because demon lords are attracted to a place to build a fortress and armies.