A large predatory mammal that can run or fight on two legs, not requiring sleep these demons were brought onto the world to create killers, in the world of werewolves these could be considered alpha males.
There is an important pair of fraternal twins. Possibly minor dieties, sorcerers, or maybe just an important pair of nobles. One is evil and one is good. The thing is, the one who looks evil at first glance is the good one, and vice versa.