Complex sentence: Doyle is a seer who receives prophetic visions from The Powers That Be, usually of people in peril; though the visions cause him great pain, his demon heritage allows him to manage them without suffering any permanent damage.
Split into simpler sentences: Doyle is a seer who receives prophetic visions from The Powers That Be, usually of people in peril. His demon heritage allows him to manage them without suffering any permanent damage.