Remember how Liz melted down the golden crown in the movie?
Anyone with Hellfire or corrupt flame can burn your army despite its fire immunity.
Anyone with Graymantle can remove regeneration.
Anyone with Vile damage can overcome regeneration.
Anyone with "Word" spells modified to ignore Spell Resistance can destroy your army due to its low HD.
A high-level fighter with a Vile Lance or Cursed Weapon can kill your army.
Anyone with Earthquake spells can kill a significant number of your troops due to their low reflex saves.
And these are just the non-cheese ways out there.