1st fight: gr can't do squat on deadman, deadman can't do squat on GR. I doubt deadman can posses GR, and even if he posses GR he still can't do squat on him.
2nd fight: Deadman wins
With the ring he can bring people that were dead back to life, created a mystical forest that Green Arrow guards now, solid energy constructs, teleportation, invisiability/intangibility and he can kill things instantly incinerating them like he did for Aquaman, Hawkman and Hawkgirl.
He also clashed with the Anti-Monitor when he had the white ring.
i know but i am asking has he mastered it as in consciously control it.
i recall DM was teleported to face anti monitor and was told by the ring to fight.. he freaked out when the anti monitor saw him and panicked and blasted at the anti monitor and then started screaming and the ring teleported him away..
I don't think Deadman needs any real experience with the ring. The ring will take over and all he has to do is point. So, I'll say Deadman in the second. 1st is a toss up, since GR can't really affect Boston.