The Lord of Darkness does not reside in any heavenly plane, nor mortal world. As Chernobog is the very evil of existence, the Primeval Chaos is everywhere at once. The traveling void of Tiarn, as it is referred to by scholars, reaches every plane of existence, even the heavenly ones. Tiarn is woven out of darkness, its surface covered by a semi-sentient black and sludgy blight. Only undead and fiends, Chernobog’s cruel children, inhabit Tiarn. 

This void of a plane was once used to hide the cosmic debris from the divine clashes between the gods and Chernobog’s corrupt minions. The Lord of Darkness took control of this plane, spawning agents of chaos and servitude, and now this soulless place is a reflection of the darkness and evil in every other plane of existence. 

To halt the Primeval Chaos is to halt reality itself— this is the eternal struggle between the Starborn and Chernobog.