The Quest for Truth

Only eliminate vampires. 300-400 of them can destroy legions on their own.

Well, you might be exaggerating... they can, of course, but there are battles in the campaign where they would be completely wiped out. Those same Archangels with their "Divine Retribution" will send them flying into the clouds while the vampires are cutting down the rest of the troops. In my opinion, the most useful unit in the game is the mummy... I carried around a dozen of them for almost the entire game)) they really helped me keep my troops intact.