The weakest castle in Heroes of Might and Magic IV!

Yes, and that's exactly the problem... because hostile magic doesn't affect a leveled-up Barbarian... but at the same time, a teammate (mage) can significantly enhance the Barbarian's combat abilities...

But you can summon a phoenix, apply some kind of dragon power = the Barbarian is defeated, therefore nature provides a counterweight to Barbarians. Summoning creatures is the most important thing. You also need a priest to resurrect the dead druid, but phoenixes will destroy the unfortunate Barbarian faster:)