Walkthrough for the "Tribes of the East" expansion.

Guys, give me some tactical advice! I can’t defeat the demon in the Wisdom of the Earth. I’ve gathered all the Orcs I could find from the map, avoiding dangerous places like the flooded temple. I bought the leaders from the wizard and I’m trying to preserve my army in battles… but this demon still crushes me. The Temptresses consistently seduce the leaders, and that’s the end. :( What should I do?