Any tips for fighting the Green Monster of the Swamp?

I’ve beaten the game twice already, and am going for a third (I’m trying to get all three endings), but I’m still having trouble with this boss. Idk why, but for some reason, it’s the hardest boss for me. Harder than Romeo, Door Guardian, Laxasia, Nameless Puppet, etc. He made me quit the game for a few weeks the first time, and it took me all day the second time. I've got the timing down form most of his moves, and keep using fire grindstones, weapons, and consumables, but I’m still struggling. Idk what I’m doing wrong. I’m about to fight him for a third time, do y’all have any tips to make the fight easier?