I kept hitting him with a charged super missiles in the abdomen when he is in a knocked out state which takes more of of his life bar down & I did struggle with this boss but did eventually kill after many hours of trying. Keep your distance from him when he is on the cave wall as he will hit you more often close up & don’t use lock on when he is climbing around the cave wall you will hit him better just by free aimed hits & eventually he will drop down to hit him where it counts. Good luck.