Here's another question - guys, has anyone tried completing the mission entirely with undead troops (after capturing their first castle)? Wouldn't that work?
What if you hire a Necromancer hero and give him the undead troops? They can weaken the enemy, and your main hero can finish them off. I did this in the 3rd mission for the Demons - the first in battle was a druid hero bought in the tavern with a fairly large druid army.