I would like a special ability that is as controllable as possible.
Perhaps give something to the Orcs, but nothing comes to mind.
How about: at the beginning of the battle, randomly places several traps. The number depends on the hero's level (e.g., number = hero level / 2). It would be annoying, but not overpowered.
I would like to see the "Veil of Darkness" as in the third game, either in the Necropolis castle or around the hero.