The Nine Hells

The Nine Hells of Baator is an outer plane in the negative energy zone, inhabited by devils and other fiends and ruled by the Elder Being Morwyn. As its name implies, it has nine distinct layers, all different from each other in geography, climate, and inhabitants. The only way in or out of the plane is through the first level, known as Avernus. From there, one can potentially find portals and paths to the other layers of the Hells, but there are no other ways to access this plane. The layer of Avernus is the home to an eternal combat called the Blood War, fought between the defending devils and the marauding demons who swarm through portals. Thus, it is a layer of warlords and warriors where the strongest rise to the top.
Unlike traditional depictions of the Nine Hells, where each layer is led by a different Archdevil who can be deposed or replaced by enterprising underlings, all the layers in this version are ruled by different aspects of Morwyn's personality. They still retain their traditional names (Zariel, Dispater, etc.) and are functionally different entities, but they are all part of Morwyn, and he can see and act through all of them simultaneously.



For more information on the Nine Hells, check out the 5th Edition Dungeon Master's Guide, page 64; Mordenkainen's Tome of Foes, chapter 1; or the Forgotten Realms wiki: here.

The Archdevils (Layer - Aspect Name):

Avernus - arid wasteland battlefield	Zariel
Dis - mountains and caverns with iron fortresses	Dispater
Minauros - acidic bog	Mammon
Phlegethos - fiery, volcanic, city of obsidian	Belial and Fierna (two-faced, front and back)
Stygia - frozen sea, cold flames	Levistus
Malbolge - endless mountain slope	Glasya
Maladomini - desolate, ruined urban wasteland	Baalzebul
Cania - icy storms, home of arcane power	Mephistopheles
Nessus - vast pits and depths, fortresses	Asmodeus (or just Morwyn)

Type

Dimensional plane