The trick is with the caltrops & its duration. You gotta slam the swords 2-3x with duration and place them right before the boss gets staggered. Once staggered, blast away with as little movement as possible. Use concealment if needs be while he's staggered. I think the attack speed + lucky hit is the better elixir (unless there are lots of adds). Should have close to 1500% vulnerable damage, close to 50% lucky hit chance, some attack speed, and lucky hit makes vulnerable roll on one of the rings. 12/12 masterworks with good slams will help a bit as well.