Developing a mage hero from the Stronghold faction.

Since Orcs don't have access to Primary Magic, you can take Dispel from the Dungeon faction and Purity from the Haven faction – these are general spells (or at least, that's what I think they're called).

I think Dispel should always be taken, regardless of who you're playing against. Firstly, it can remove two general enchantments from multiple stacks simultaneously. Secondly, if there are only two stacks of champions left in the final battle, casting Restoration and Stone Skin on your own units and preventing the opponent from doing the same can help you win the battle. Purity is only useful against mages.