[Micah]

You might want to try out a bunch of Abominations and Tartarians, back them up with an Army of Lead to bump them up to 20+ prot and 22+ MR and maybe a mass regeneration. That will spread out the mind blasting and soul slaying among a lot more high MR targets than trying a lone SC, which tend to blow up on a bad roll, and are a much bigger investment. (And are susceptible to Vengeance of the Dead every turn if they do live through a significant battle, cast by all of the high-penetration mages in the capital). Have the leader avoid killing anything for just that reason, and have a stealthy astral mage follow the army around to stop mind hunts. Empower something stealthy if needed, since getting him in combat will get him magic duelled to death. I think giving him MR items will help keep him sane so you can keep everyone together. Tossing in an SC with magebane/lead shield/amon hotep/armor of souls (or rainbow armor if no blood)/amulet of antimagic will give you a 41 MR, buffed to 45 in combat, which might be a good idea as a lightning rod, since the chance of beating that even with 10 points of penetration is vanishingly small.

Also try to take out his temples via raiding, he's likely going to have a hard time replacing them between freespawn upkeep, pop death, and his actual mages and mind blasters if you can keep him from taking new provinces over. You'll want to keep his dominion out of your lands and if possible to push his back. Blood sac if you can.