This reminds me of a game called \"Lionheart,\" where a demon possesses your character, but can cast spells for your character.
First of all, I like this idea. It\'s unique, and gets rid of the overused system of mana. Not that I detest the overused system, but uniqueness is what Planeshift aims for. I think. In any case, I like uniqueness, if only because its different.
Anyway, I think that the Spirit would have to come back to the body, instead of the body going to the Spirit. It\'s more convenient, that way. Also, maybe only a specific race (Diaboli?) actually does turn into a demon, or only specific characters that go through a specific ritual can. I don\'t think that many people will enjoy watching their character turn from a wise sage to a bloodsucking fiend of nature that happens to be hungry while teaching. While this, in my opinion, may undermine the system of old sage wizards, perhaps something can be used to keep the old sage wizards, but also include Spirit Power. Such as a ritual.
Don\'t ask me to change the name of Spirit Power, I\'ll only come up with worse.