grandmaster is the easier of the final bosses, your build was just a mid game build, not an endgame one
??? mirror shield should've made that a cake walk, just alternate between shielding and hitting him with single cleavers and he gets no rage and no spikes
You can still win with cleavers, I just had a cleaver run that made it to floor 18 and only died to my internet cutting out and the page reloading
You could either out damage the bees or get cleansing items to beat posion easily.
if you're using cleavers you can just use one at a time, it's a bit of a pain but it's not an absolute brick wall