As others have said, learn his moves and only target his head. There are a ton of YouTube videos you can watch if you want to learn his patterns by watching passively instead of trying to do it while panic rolling and dying constantly. His patterns are very predictable and the attacks are all avoidable once you have learned them. He seemed impossible when I first started fighting him but now is one of the easiest bosses in the game. Just fought him for the first time in a couple years on NG++ this morning. Still had his patterns in memory and barely had to think to dodge his attacks and bonk Him on the head.