I found it easiest under 30% weight and with a fast weapon (I used a scythe and was naked). Learn his moves, they are pretty simple to learn and as long as you stay behind him you should be good. On his second form you have to be quick to run away but you also need to be quick enough to close the distance (never let your endurance go to zero). I prefer to stay close to him on his second form, but you have to wait a little longer before you attack to guarantee he won't hit you. Don't roll too early in this phase, the lag on his attacks are crazy and they come out slow.

I always prefer to roll into the attack, whichever direction it is coming from, and I always made sure I had endurance left so I could dodge if I screwed up. Lots of times I would keep dodging his routines until my endurance bar was back to full, because I regularly had to dodge-dodge-attack-dodge (something like that) and if I ever ran out of stamina it could be very costly. I sometimes would hit him twice in a row in his first phase, on his second phase I would only hit him once since he does so much damage. The second phase isn't too much different from his first, just remember his attacks come slower and are actually easier to dodge if you can slow yourself down as well.

The main two things that helped me: 1) slow my reactions down in the second phase, just calm down and realize his attacks are actually easier to dodge, but now they have to be dodged perfectly. 2) A fast weapon which doesn't use a ton of stamina and allows me to dodge 2-3 times after I attack.

For what it's worth this dude wrecked my face for two days, then I nearly perfected him once I got my timing under control and found the right weapon.