Why, because I called the antagonist(s) demons? That's not really much of a spoiler given the OP stated there is a creature such that if you look at it you are driven mad to suicide. So you already knew from the OP by implication that there was likely a supernatural, mind controlling, hostile and and evil being that drives people to terrible acts of violence and murder. Others referred to it as a "monster" before me. Maybe you would have preferred that? If you feel any better, they don't go out of the way to declare that these things are in fact biblical demons or something like that, which is why I put a question mark after "demons." Supernatural evil being, monster, evil creature, demon.