This special ability was in the game. It wasn't scripted.
If you increase the damage of Cold Steel, it will increase for all heroes who learn it.
Yeah, it's tough to come up with new special abilities. Is there a general description of all hero specializations somewhere? Maybe I can find something to base my ideas on. By the way, here's another one: Philosopher's Stone - The more crystals a faction has, the stronger the hero's attack and defense.