Question to people who have done the 1 tank soak method on Twintania.

I am a bit confused on the part where we must kill all Hygea together with a mage lb. How do you ensure that Ascelpius gets the 4 stack debuff but the MT avoids it?

Is there a way to LOS the debuff or maybe sprint at the perfect timing to out range the debuff as the hygea die simultaneously near Ascelpius?