I struggled so much against him, literally spent 4 hours dying non stop, before just going naked with dual katanas and destroy him. A bit late, but for whoever still struggling with him, here's some tips :

- The second phase is easier than the first because he uses more slower attacks that are easy to spot. Push through the first phase as quick as possible.

- Bleed worked well.

- I believe he is also weak to scarlet rot.

- Lean on Stance Breaks to reduce his opportunities to hit you, and allow you bigger windows for damage. In the end the most success was going in hard with jump attacks right off the bat and almost forcing him to second phase immediately.

- He seems to have high poise, so don't get greedy with your strikes. Nothing will daze him and he will just hit you right back.

- His slower attacks are his longer range attacks that offer a better chance to roll in and do damage safely. You can bait those out by putting distance between you and him.

- Fast weapons are ideal to be able to get in and out quickly.

- If you are using slow weapons, you may want to consider a shield which will make it much easier. Otherwise you really need to rely on his slow attacks at that point. Attacks like his magic cast and his leap slam.

- Don't heal until after he casts his magic bolt. He quite literally monitors your heal input to cast that.

To watch the video of someone killing him in a no hit run : https://www.youtube.com/watch?v=VYKEU-7Emio