It could be made even more interesting!!! For vampires, reduce the amount of life they drain based on the damage dealt (i.e., not 100% of the damage, but at least 50%, and if the hero is a vampire specialist, then 80%).
BUT! Add the ability to transform an enemy creature into a "lesser vampire"... i.e., if a vampire's attack on a group of creatures is the final blow, and the group dies, some of them rise on the side of the Necropolis with reduced stats and a slightly altered appearance... and, of course, at the end of the battle, these creatures die from sunlight:) That would be awesome!!!:))) In any case, the Necromancer's war tactics would change in that case.