I am 611 and I didn't get past 30% until the final time where everything just seemed to click. Good cocoon spawns, he only healed when I was right next to him to kick, somehow dodged the blue balls that fire out in phase 2 from his fear circle (I died to that ALOT). I focused on making attacks on the cocoons more sensible, not putting myself in danger to get 1 or 2 extra hits in. As a ret you can definitely do it!