Well.. judging by the title of the topic, I probably would disagree with it.. Adding 'demons' seems like a lot of work, and it's almost like a creature, yet more special. Therefore rare. And how would one come to possess one of these mythical and sacred beasts of a demonic nature? I'd expect one would have to be evil, and rather strong to be able to control the demon's power and desire to take over. The demon would probably require special treatment and special goals or sacrifices just to keep it satisfied.