Very annoying to cut off need good timing on breaking crystal so he's stunned and getting good tries at the tip of his tail so it cuts off are the best tips. Even then it can be a real pain. Cutting the tail is harder then actually killing him, heh.
Its really very simple. Run over to the crystal to aggro him that way. When he moves his head to start his attack, begin sprinting to your left. His attack will break the crystal and stun him. Get to the tip of his tail and cast 2-3 great combustion(based on level of pyrohand and playthrough variables). Easy peasy lemon squeazy.
[This message was deleted at the request of a filthy casual]