Umbrals....

[Endoperez]

Except if Agartha gets Army of Gold up. That stops the fire damage nicely. On the other hand, Army of Lead would boost their magic resistance, negating control undead...

I don't think Umbrals are cold-blooded, but the living Agarthans are. Cast Wolven Winter where you're going to fight, and enjoy horribly screwing over Agartha's mages.

If you can manage to collect something Umbrals can't hit and can't drain life from, you're pretty good. I don't remember if their attack is magical, but ghosts or other quality death summons should do nicely.

[vfb]

A few golems dual wielding Eye Shields and Charcoal Shields, with Boots of the Behemoth, might make a good defensive line.

Eye Shields are always a good plan versus Agartha.