I fought Grym and it did not even occur to me to lure him into the forge hammer at all. Just suffered through only one character being able to really damage him because he had a bludgeoning weapon. My partner was so bored. Then we beat it and got an achievement for killing him without using the forge hammer and lost our fucking minds. On second play-through, tried the hammer thing and he just would not fuck around with the middle of the platform at all, so I, again, just had to bludgeon him to death (but I came prepared and had bludgeoning damage on all my melee characters this time, lol).

Honestly, it's a neat idea for a fight, but it feels so out of place to have a mechanically scripted fight were you have to learn boss mechanics to do it "right", all alone in the middle of a sea of loosey goosey "how do you want to do this" amazing nonsense fights.