Stygia

The fifth layer of the Nine Hells is a freezing realm of ice within which cold flames burn. A frozen sea surrounds the layer, and its gloomy sky crackles with lightning.
Archduke Levistus once betrayed Asmodeus and is now encased deep in the ice of Stygia as punishment. He rules this layer all the same, communicating telepathically with his followers and servants, both in the Nine Hells and on the Material Plane.
Stygia is also home to its previous ruler, the serpentine archdevil Geryon, who was dismissed by Asmodeus to allow the imprisoned Levistus to regain his rule. Geryon’s fall from grace has spurred much debate within the infernal courts. No one is certain whether Asmodeus had some secret cause to dismiss the archdevil or whether he is testing Geryon’s allegiance for some greater purpose. (https://www.dndbeyond.com/sources/dmg/creating-a-multiverse#OtherPlanes)

Alternative Name(s)

Fifth Layer

Type

Dimensional plane

Location under

The Nine Hells

Owner/Ruler

Levistus

Ruling/Owning Rank

Archdevil

Characters in Location

• Levistus