I base this entirely on the Dresden Files, where horrendous creatures like the naagloshii, or skinwalkers, ancient evil shape-shifters that pervert nature with their very presence, feed upon the fear they cause so much that merely speaking of them gives them power, love torturing so much they rarely kill their pray unless it can make another suffer making them watch, and unable to be killed or banished by magical or conventional means without either ancient Native secrets or a test nuclear bomb… are kept the in the minimum security section at a magical prison the original Merlin created.