I was thinking a bit, and looking at this power in the custom powers section gave me the idea for a challenging and fun character to play: A spirt stuck in some person's head.
Bound Spiritual Entity [+3]
Description: You are a spiritual entity imprisoned in a physical object, you have no body, and cannot act in the physical world without a bearer.
Effect:
Unbodied. You cannot take physical skills, you cannot move yourself, and you cannot communicate verbally and other neat things.
Communicate with Bearer. You are able to telepathically speak with the bearer of the object you are tied to.
License to Possession. If you have the domination ability, you qualify for the possession upgrade, and you can possess your bearer.
Called to Bearer [-1]. You have the ability to tie yourself to the bearer of your physical prison, and you can teach them to call your prison to their hand.
Switch the "in a physical object" to "in some dude's head" and give yourself a couple powers I made up:
Empowering Spirit -1
You cannot take powers yourself, but you can give them to the person you are bound to. Any powers/stunts you have (unless they say otherwise) are conveyed to your host.
Creature of Spirit-1
You have no body, and as such, you are unable to be "hit". Eliminate your physical stress track and add 2 boxes to your mental stress track. Magic made to target spiritual beings can hit you, and fire can damage you, but you take it to your mental stress.
At this point you can give your "bearer" powers in order to assist him/her. Maybe you have the ability to take over your "bearer" in a fight, and assist hiim. I think this would be really fun to play.. please give your opinions.