I'm currently playing with a friend, we're both level 25-26, on a huge map with an underground. He's playing as a Barbarian. We'll both have super skills, meaning we have a teacher.
He's very confident in the Barbarians' invulnerability (and Barbarians really are overpowered), but I decided that the only foolproof way to kill a pumped-up Barbarian would be... Divine Retribution + a lot of meat. Accordingly, Creature Ability + expert light + a Revenge spell bought in the shop for 15 crystals will do its dirty work :)
Moreover, the first half of the battle will be standard - I'll be casting mass buffs, and he'll be killing my units in packs. He'll find out about Revenge in the second part of the battle, when I start taking out his stacks one by one :)