So after reading the page for this guy, i was fully prepared to get destroyed by him multiple times. Died twice in a row to chained gunfire, but did well before being annihilated. Third try i killed him no problem. Char lvl 71, arcane build. The easy, no nonsense, safe and fast way i found for taking him down was the beast cutter- he simply does not understand how to deal with the transformed r2. Stay locked on, walk backwards, and he'll follow you. Keep him on the far edge of the r2's hit box. Use r2. He wont dodge a majority of the time, he just walks into it and eats it. Old hunters bone? R2. Throws something? R2. Just dodge when he dodges to avoid the pew pew spew, and then yeah.. R2. Did not intend to cheese him, but when I realized it was working without any effort i just kept going with it. So there you are- if you don't feel like stair cheesing etc, you can always just, well, r2..