A politcal and/or religious egregore with an agenda. The core program of which consists of religious doctrine and survival instincts, Kinda like a rogue AI surviving on worship and fear. Least this is my understanding of the matter.
Haven’t tangled with any of the Zoroastrian ones yet. Im not that stupid… Heard of one guy who ignored the warnings in the book about prep work and he ended up in an asylum for awhile apparently.