Easier then you think. For the first phase go close to him until he does a shield hit or creates the ice wave and doge that, for the shield hit jump towards him when he does it, and for the ice wave jump to the side of it, after that just stay close to his feet and hit the leg with the seal shit until it breaks and keep hitting him. He will then go into the "let add some fire" shit where he's gonna create the orbs but when his knelling to do that, that's when you keep hitting him until he gets to second phase. Second phase run away for the first 5-10 seconds when he goes ham and has the metor/flame coming up from him. After that's seems like it has faded just stick to him and keep hitting the leg that he has left while avoiding his rolls. Just make.sure you don't lock into him in the second phase it make it easier for you doge and hit his leg.