Why dont you just surround him with all of your characters and when he stuns your tank, stop dps and have consecration + greater blessing of salvation spam on mages to pull threat back again? Seems like you are wasting so much time running around (gbos because it can not miss or be resisted like other spells )
Your mages are getting one shot, cast consecration (rank 1) with your healer so he takes the hits instead of mages when the tank is stunned, use devotion aura+concetration aura + ice armor on mages
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