@Igmkjp: Okay I think I got it. Try the Dex build - max out Agility > Intelligence > Body > Perception, leave out Strength (which is also left in Corrupted stage). When you rush down the boss, whittle them down to 70% (threshold just before they start the heal move), start with Specialist Strike and autocast every Dex move you've got. Worked twice for me now, and you can stack Perception in this form to 30% crit which works great for Dex rushing.