[thejeff]

I'm more familiar with the later Arcosephales. Wasn't it an astral nation in EA?

Try Charm as well. It's nature but short range. If you can make it work, they'll fight for you.

Air Magic? Thunderstrikes are good if you can get a lot of them. Fog Warriors might help, but not if he's got a F9 bless.

Against Neifel giants, single target one shot kill spells are what you want. They regenerate too fast to try to whittle them down.

Fires from Afar will damage a few troops. It'll kill normal humans, but the giants are too tough.

Breath of the Dragon does poison damage. It's nice, but does damage overtime and it probably canceled out by their regen.

Tougher/higher protection human units will still die in one hit so they aren't much use. Go for numbers but only as a meat shield. The mages do the killing. Massed summons can work too. Vine Ogres can make a decent wall. Living Statues or Mechanical Men if you've got the Earth magic.