Late age R'lyeh vs Ermor

[Taqwus]

The free H3 priests are a nice bonus, and the freespawn can provide a meat shield.

Consider the old tactic of drive-by banishing to attrit them -- banish and run away.

Get a fire mage if you can, for flaming arrows. Regular arrows won't help much nearly as much against a front line of cheap dispossessed spirits or ghosts. If the Ashen Empire shows up with a horde of ghouls and ghosts, forget about the idea of mindblasts locking onto commanders for an easy victory.

Boots of Quickness + Herald Lance = 2x Solar Rays/turn + local morale boost. Not bad if you have a mundane commander.

A Vastness's Blood Vengeance can wreak havoc on low-MR freespawn undead in melee, and will punish the commanders of any army composed almost entirely of mindless units.