NHF – new heroes for Heroes V 3.1.

By the way, I'll rework your Hafad: I'll make his ability work on heroes too, even if they're in the town.
You can, of course, do it yourself. You'll only need one function without triggers and forced interactions.

It will just be incredibly overpowered, I'm afraid, and that's too much for Necropolis. They already have high magic and ghosts, plus the largest armies in the game, so they can easily finish off weakened opponents.