[Legendary League]

If you want to defeat Ermor, you throw Undead Mastery, Solar Brilliance, or other major battlefield evocations (like Firestorm) at him.

Or you can cast Pugatory and annihilate his armies without even fighting. Purgatory just destroys Ermor. You then combine Purgatory with blood sacrifices to slowly but surely push back Ermor. You could also throw Astral Corruption on top just to spite his mages. And combine that with major SCs who can eventually run out the timer for his army.

Wait a sec, that's what I would do if I weren't being unjustly attacked by Bogarus.