Been romping with my Undead until...

[Saxon]

You may also wish to get a nice squad of undead horsemen. Put them as far forward as you can, on the extreme left or right. Make their battle orders to attack the rearmost.

The effect is that they will race down the side of the enemy army and hit those hiding at the back, who are usually the priests and mages who are hammering you. They will quickly take out the commanders, especially priests, making your un-life a happier place. This also creates two targets for the spells, which reduces the effectiveness on the usual closely packed troops.

I also put my other regular undead troops as far forward as possible, so they get into action earlier. Leaving them at the default starting position means they are exposed to “spell fire” for an extra turn of two.

The earlier suggestions on protection spells are very good. I am currently in a nasty war with Ermor and toward the end of the battles, when they have protected most of the surviving troops, my banishment power goes way down. Those protection spells work! On the plus side, I have five priests in the hall of fame, as their kill count is truly massive. I am boosting them with precision items and they get even more dangerous.