NHF – new heroes for Heroes V 3.1.

Maybe they could just not give her demons, and come up with something else? Like, the attack of creatures increases if they fight against "evil" races.

Dark genius.
All spells from the Darkness school cost 1 mana less for every 10 levels of the hero. In addition, the hero learns the Grief spell (common).

Hunter.
The hero can place traps on the map. If an enemy hero falls into it, he may lose an artifact/part of his army. The probability is 10% + 2% per hero level.