[Groundworm]

Thank you for the excellent suggestions. I was finally able to defeat his mages after multiple battles that whittled down his chaff (serpents, sirrushes, lizard infantry). This allowed my mages to target his mages early, and I killed several of them in the first few rounds with well-placed thunderstrikes. He still managed to summon a lot of skellies, but between my priests and several hastily-forged herald lances, I was able to kill most of them.