I find most of the ACT III encounters to be poorly designed most likely due to the crunch to get the game finished and lack of playtesting. The whole "Unstoppable" nonsense is a real turnoff and seems like a band-aid attempt at increasing difficulty.
My least fav in the whole game is the Netherbrain fight starting with the dash up the stairs right to the bitter end. Just a lot of gamey gimmicky stuff, winning brings a sense of relief instead of satisfaction, and there is not enough variety in ways to beat it (which is the best part of so many other fights in BG3).
