I know this isn't how Mantels work, but...

It occurred to me this week, that if you think of them being akin to a Venom type symbiote, their a lot easier to understand. They give the wearer powers, they can change their appearance (Kringle), they try to convince their host to behave differently, and they can be transferred, under the right circumstances.

And if they ever do another Dresden TV show, I want to see Harry actually arguing with the Winter Mantle!