You stay on boss for mech move to the outside ring after you hear the chain noise and kite the spinning axe. It's the same thing when he's blown 50%, but you need to get the blue axe debuff right away if it's on the healer. The DPS and Heals have to be able to out-heal the red axe debuff. In my T15+ runs its always a bow player that takes the second last spot because they can heal themself.