[MaxWilson]

I can think of a couple things. You say you have access to E1 mages. With three gems, an E1 mage can do , which gives all the Abysians on the field rusty armor. Unlike Destruction it doesn't work with archery--you actually need to hit them in melee to destroy their armor--but combine it with your elite Sauromatian cavalry or even enough chaffy militia and you should do serious damage in melee. Abysians have lousy defense, they rely only on their Prot, so by making it rusty you remove their only real defense except for their heat aura, which takes time to work.

Also, you have strong national access to death. Cloud of Death is a beautiful spell against heavy infantry, since it does 9+ points of damage in an area and ignores armor. Skelly spam (Raise Skeletons/Raise Dead) is also good, since the Abysian infantry have high encumbrance. They'll beat down the first few waves of skellies/zombies but after a few waves they'll start to tire. If you can get up to Alt-8 every single D2 mage you have can spam Disintegrate, which is cheap and nasty.

There must be some fun things you can do with communions and Nature/Water magic on your national mages, but I can't think of them offhand. Do cast Will of the Fates during battle if you can, and your Nether Dart spam idea sounds good. Do fear Flames From the Sky if he builds up enough fire gems--you may want to keep your armies dispersed so he can't hit them all with the same spell.

Don't fear assassins, just give your most important mages a couple of guards each. Mages usually do quite well against assassins anyway, especially death mages who can cast Raise Skeleton.

-Max