The “An Eye for an Eye” scenario.

The simplest option is to make Lethos your main hero (and make him a supporting hero in the scenario) and develop his summoning skills. While the huntresses/beastmasters are in invisibility, the phoenix can decimate the enemy army. And high-level Dark magic isn't a burden – with "Berserk" and "Dominate" skills, the task becomes extremely simple (just find a Dark magic spellbook).