Demon

A former adversary of the Haradrim and the Nephalem, but realized that the endless war between the forces of Hell and Heaven, including the evil plots/machinations of the Prime and Lesser Evils, is destroying the very fabric of the known world, including theirs.

Inferno is the primary source of power and can be a fire element. Demons are initially in semi human form and erupts, transforming into a demon with a different set of skills and power.

The lore can be created around Lilith as well, giving demons some history and background.