Body riding spirit - communicate but no control
 

Hello GURPS gurus, I'm in need of some help. I've searched the forums, but 51 pages of 25 results each is pretty daunting and I'm not sure how to narrow down the search to find what I'm looking for.

I'm trying to build a spirit Ally that has the power to jump into a living body within sight, but doesn't have any of the mental or physical control over the creature. Very similar to a spirit of intellect from the Dresden book series since it can communicate with it's host. It's also supposed to be nearly impossible to exorcise out of the body against its will.

I looked at possession and it doesn't fit entirely from what I can see. Spirit advisor from Gurps Mysteries seems to be the closest fit, but I want more control than it just being an NPC.

I'm going to also use it to grant my character some powers by way of a pact. The spirit doesn't possess these powers inherently, but is essentially giving away part of its life force.

Re: Body riding spirit - communicate but no control
 

Granted by Familiar can work but from your description the limitation should be a lot less since your Spirit Ally is far less vulnerable.

For the Possession thing you could try a limitation on Spirit Possession with an enhancement to protect against Exorcism. Parasitic has a nasty downside.

Another way though could be Permeation (Flesh) and I would add a new modifier.
Ride Along
You are able to yourself to whatever you use Permeation on so that you move along with it, however it moves. Your weight does not count as encumberance and this cannot be used as an attack or to cause harm, though you do count as touching for purposes of other abilites, either yours or the one your riding. +20%

Re: Body riding spirit - communicate but no control
 

Yeah, Possession really looks like the logical way to go. I think this might have come up before, although a quick search didn't turn it up. You'd want to borrow Sensory from Mind-Reading and turn it into the Sensory Only limitation. The usual value so derived (-80%) looks too generous a discount to me, though.