The weakest castle in Heroes of Might and Magic IV!

I don't see anything wrong with using fairies and minotaurs.

Well, it only seems that way at first glance...
because you understand that in offline mode, a minotaur cannot be killed by any unit.

and a single fairy can defeat any number of dragons.

IMHO: the fourth game is not suitable for offline play. Online play is a completely different matter. ;)