Shadowwyrm from the shadowfell
Urishtar Nightwyrm discovered an ancient structure in the Shadowfell constructed by the Raven Queen of death. Urishtar claimed this structure for herself and renamed this place the Nightwyrm Fortress. Within she has learned a lot, probably too much, about the passage of souls from life unto death. She has learned to diverge their souls and harvest them into energy of her own preventing souls from ever reaching their final destinations.