The most challenging campaign.

It's tough on Biara, but I only used Zehir's spells, namely: Armageddon, Holy Word, Divine Vengeance, and the equally awesome spell, Banish.

Banish didn't work very well for me. It only seemed to banish Archdevils one at a time. Apparently, Biara's magic was the deciding factor. I mostly relied on hives there. I placed them all over the field using the Sign of the Magician and slowed down the demons. Divine Vengeance also worked well.