Spiritual Possession

Spiritual Possession describes the unique nature of Possession (advantage) B75 using the B76 Spiritual limitation.
Firstly that it requires Insubstantial w/ Affects Substantial.
It's pricing seems to reflect the sum of taking Only While Insbustantial and Substantial Only on Possession.
Due to possession requiring "touch" this is best reflected as a grapple prior to using Concentrate to initiate the ability.
Insub v sub benefit is they can't Break Free of it, and you can tag along for a ride until the ability succeeds...
Except of course that resisting Possession gives immunity! But that's now how ghosts work!
To reflect how ghosts can brute-force possession through repeated attempts, this requires PU4p13 Reduced Immunity.
This would have a side benefit of also decreasing something unique to Spiritual Possession: a 24 hour embargo when exorcised.
"Permanently immune" is level 4 and "Immune for 1 day" is level 3. So you could buy 3 levels so that exorcism gives no immunity whatsoever, while a successful resistance gives a cumulative -2 penalty for the next hour, which is probably pretty realistic (attacker loses confidence, victim gains it, etc)
If one wanted to make these cheaper via Limited Enhancements, you actually save more points by applying "Costs Fatigue 5, -25%" to +150% worth of enhancements rather than the base ability!
"Maximum Duration" doesn't fit GURPS Spirits, there's no such thing as a 5 minute window of uselessness, even though it's a great way to save points. The closest is how crit fails neutralize the ability for 3d days, but that's better covered by Crippled Powers.
Maybe the way it ought to work is using Affliction (Puppet) and having it be Puppets-only. That way you don't roll for possession (meaning you don't need Requires diff: will enhancement, save points!) instead you roll for Affliction, and you can pay for extended duration that way.
This could be bought as Followup rather than Link to save points.
Category:Concepts