Problems with Heroes of Might and Magic IV.

It's really fun when your entire stack gets wiped out.
And for every unit, there's a counter in the fourth game. For example, against the Great and Mighty, you can find a simple and unexpected answer, either a Death Ripple spell or a similarly sized group of Swordsmen (or whatever they're called, Crusaders). For a vampire, Black Dragons will be scarier. :)