Im playing on tactician difficulty, and it was such a clutch for me, I used the orge horn, they were useful for distraction, then used my barbarian with tiger heart to kite the Grym to the middle and after pulling the lever for 3-4 times I finally finished the battle, all my characters were below 10hp and 2 were downed by the end.
The hard part is he'll go after whoever pulled the lever and since he just got up from the center there isn't really anything you can do to avoid and attack from him.
It is my last task in this act. The last big boss. I had also the idea to leave one member on the stairs above to shoot down the spawning elemtars, but havent tried it. Grym gives me trouble as soion as he gets up from the first hammer hit. I cant get him positioned again underneath again. He almost zooms from one end to the other of the arena (almost) and misses everytime the hit area for the hammer X / Obviously he downs two of my team and killing them effectively, becaus ethey ar eout of reach for me by that point. (and some how the resurrection scrolls arent working as Ive thought. Im getting the message "target obstructed" while standing directly in fron of the body )
Spent ages trying on this, finally did it by making him chase one end to another and getting him hot, got him down to 18 then Harold doom bow finished him off. Lost Lae'zel but it was worth effort
