This is sort of a monster I had an idea for independent of Dresden Files, and wondered how to pull it off. Because it relates to Magic, I'm wondering how it might work, let alone if the Council would get windo fit.
It's sort of like mortals making themselves into something like Red Court vampires, but not.
You have mortals who use blood for "Blood magic". This blood allows them to do things to themselves, typically using supernatural physical powers (strength, speed, etc). To do this, they invoke a Totem - not necessarily a Spirit, but they tap into the existing nature of certain blood drinking animals to get the ball rolling. Ticks, mosquitos, leeches, flies, that sort of thing. This slowly changes their appearances to mimic their totems.
So you might have a humanoid with wings and a probosis, or change its hand into a leech, able to take a beating. They can crank up their physical prowess by tapping into the power of the blood they store (like Red Courts and the blood in their stomach). So they very well would have a feeding dependency for their powers.
