Again, Rifts. This time from Wormwood.
Ah, I saw that shudder! Hehehe. Yes, Wormwood was a scary, scary place for that RPG setting, with the Apok being one of the few truly heroic figures fighting against both hopelessness and corruption, from both within and out.
There are a few demonmask ideas that came about after flipping through the book the other day.