Well, I have one idea in the mind:
Nazgrel calls a spirits of fallen warriors from the dead bodies lying around adding X*number_of_corpses armor and X*number_of_corpses life regeneration to the allied units in 700 range.
Fel version would have same basics, but instead calling spirits it would make corpses explode dealing to enemy damage and lowering their armor.
Now, I will go back to the campaign - in Orc3 and Orc8 giving computer to the player is definitely BAD idea - it totally would break the balance, because AI acts in specific ways doesn't really cooperating with player. So that SHOULDN'T be changed. I can just imagine human knights and priests cooperating with orcish army and I definitely don't want to see that as true...
And of course, I'm against giving control over Cairne in Orc2, but I don't think I will be stubborn here. Using Cairne in O2 isn't important and breaks system a bit. First of all I would like more to have fun with new hero one scenario longer, also Cairne becomes playable in Orc6 and that doesn't need to be changed. And, last of all, Cairne played by player and Cairne played by AI that's two different Cairnes, so... maybe let's leave this, as it is?