I'm a mage and we tank both of them on top of each other.
All dps has the dark essence and we're dpsing the white one.
We're all bunched up and staying on such a position that you only need to click to switch to white essence, portal is right next to you.
When the dark one gets the shield I:
- Click the portal
- Pop Presence of Mind
- Shoot Arcane Blast
- Pop Arcane Power
-Spam arcane blast
By the time I get to the spamming it's already the fifth second of the cast.
It might be a bigger dps increase if I just skip the presence of mind + AB but I cba to do calculate anything right now, the shield go down!