If you're Playing Dresden in North Bay, ON, READ NO FURTHER.o.k, so I have an adventure idea that revolves around a shapeshifting party member.
A bad guy summons a demon to get it to do nasty things. In return the demon wants the freedom to do as it pleases (this is a very, very rough explanation of the pact)
My idea was to have an entity who attracts shapeshifters in a large area to him(several kilometers radius)and "forces" them to want to shift into their particular forms.
The reason the entity does this is because he's stealing their "human form" so that it can eventually walk among the mortals without having to use his energy creating a physical form for itself and no longer needs to rely on its summoner to stay in the mortal realm.
Everytime the demon forces shifters to change form, it steals their human side, eventually leaving their animalistic sides behind.
So a shapeshifting wolf, would become a wolf always. Or, for instance, a human who gets an aspect of the wolf during the full moon would run around thinking he's a wolf during the full moon, but any other time of the month he'd be catatonic because there would be nothing human left.
So how do I do this?
One way I was thinking of giving the PC Plot driven "involuntary Change" and tying it to an aspect. (he'd get an extra refresh until they solve the mystery or until he's driven mad)
I was also thinking of giving the demon a form of "incite emotion" (to get them to want to shift) and " eat power" to steal abilities...but you can't really steal non-abilities, ie: humaness
I want to give the PC (and the other shifters) a discipline check to resist the compusion which gets harder everytime they are affected. So another way, maybe, is a spell that causes mental damage, with consequences that I can compel like, "must go hunting" or "wants to be a dog" etc..that way they can slowly insane and when they get taken out it means they've been fully transformed. But what kind of spell would that be and what would the mechanics of it be?
It would be cast from a Place of Power at the very least.