Infernalism

Infernalism
Following the Cad Goddeu, certain dark gods were vanquished by the Celestials to the void or abyss. This region, the True Dark, was separate from creation itself except through a connection to the underworlds including Annwn. The Celestials forbid the fae and humans from worshipping the Dark Gods. The fae that disavowed the Court of Seasons were exiled and retreated to Annwn and the service of King Arawn. There they formed the Shadow Court and in both the Mythic Age and the Age of Man, the Shadow Court spread the worship of the Dark Gods among humans and actively sought to destroy the Sons of Dôn.

A mundane human can be an infernalist via religious worship. Satanic cults are one form of infernalism. More comonly, black magicians and Shadow Court fae are infernalists and intentionally empower the True Dark through ritualized acts of intentional violation and defilement to feed malfic spirits which in turn increase the influence of the Dark Gods.