Is the power they bring really worth having your body become a play thing?
I created a game called Noughts and Crosses which is all about conflicting interests and using power over your morals. In the game you play ordinary people who are in touch with another conscious. This could be anything from an ancestral spirit that has watched over your family for generation to something more sinister like a genetically engineered symbiote that a mad scientist injected into you.
Whatever the reason, you hear voices in your head. Sometimes they help you with powers beyond your belief but nothing is free. They have goals of their own. Each time they help it becomes easier and easier for them to take control of your own body.