lolz GR crushes Jason in every way possible!
possession isn't even in the equation when it comes to Jason's worm demon.
GR is powered by Zarathos. A powerful angel of Justice that protected Earth but was tricked by Hell's armies and fell and became insane. A Spirit of Vengeance emerged and for aeons rode the land crushing all sinners with little retaliation.
At the end of the recent GR he re-obtains Zarathos' form and proceeds to wreck havok. He is power! Justice personified!
Jason don't mean shit, nor the demon inside of him. He will be destroyed the instant GR even recognises his presence.