Pre death version of Sentry
Hum. I mean on just a very basic level I'm not sure there's anything in any lasting sense either can do to the other.
edit: I presume you mean Kuurth at full power, not Kuurth after Cyttorak created the Colossusnaut.
Then yeah, there's not much either is going to manage to the other up in this piece.
I know they tried a variety of attacks on him, like setting his blood on fire, but did anyone try to just turn him into a turnip or something?
Considering the variety of stuff Kuurth basically bounced or ignored or instantly countered, I feel like transmutation/that kind of thing working on the dude would be a leap.