I very much like how the Troll Killer functions, actually. They wouldn't die due to their crocodile-scale shield or elk-rib coat, or because they're Lucky, or because they're relying on their Honed Instincts. Maybe they're Fearless, and can draw a monster out and expose its weakness. Or it could just be because they rolled well on Hold Steady to stand strong against the beast, and gain +1 forward. Beowulf took his bearings, asked where he could go unnoticed, and feigned sleep when Grendel entered the great hall, then used the +2 to his rolls he got from Honed Instincts to surprise the beast and twist its arm off. He did the same thing later, but his "What does this place have to offer me?" turned up the magical sword that he cut down Grendel's mother with.

I think it's a very well-done playbook. Certainly not Conan's playbook, though, and I'm not sure it should be.