[Executor]

Earthquake, rain of stones, firestorm, solar brilliance, undead mastery.
Purgatory, Flames from the sky, Wrath of God,
AoE heavy spells if you have loads of mages, fire cloud, wither bones, cleansing water, conflagation, magma eruption. Having precision spells for those helps.
Items such as heralnd lance given to commanders than casting quickness on those commanders so they cast a bit extra, or give them quickness items if you have gems to waste. Bell of cleansing, massed bows of war, also under quickness, bringing along the forbidden light artifact, using aegis (probably the best option for massive hordes of undead).
Thugs and SCs. I recommend kitting those WrathLords with a luck pendant, and as much defense as possible. Items like, vine shield, faithful, cat charm, chain mail of displacement, boots of quickness and such. You can also bring a few mages to cast one or two buffs on him and retreat. Like Micah said just keeping him around until turn 50+ is enough.
There are pretty much dozens of thugs and SC you can use with any nation. Just have enough defense, and buffs like luck, body ethereal, mistform, etc. I suggest looking up some thugging guides if you`ve never created such a unit.

And many, many, many more things...
Also I suggest listening to Calahans advice. Fighting the AI offers no chance for improvement. And MP games are easy to join, are and can be played under quite relaxed schedules and are immensely more fun.