[Meglobob]

If he is using a communion cast rigor mortis. It will fatigue out his mages quicker, meaning you face fewer spells, hopefully send all his mages over 200 fatigue so they will die.

Attack rear (straight away with flyers) to get at his mages. Ermor has A1 on some of its mages? Cast flight on your banes and have them attack rear. Put your behemoths up centre front with attack closet, try to luck them to help them survive longer.

Cast darkness if you can as well. Have your mages spam steller cascades/ghost grip to fatigue the enemy quicker.

All that should bring you victory.