Since there is already Lightning Fist in game I think there should be other elements.
They wouid all give the same damage and attack speed but have different effects. They would have the same cost as lightning fist. With a limit of 1 Fist so they have to choose which one they would prefer. Have a Single target, bounce and aoe.
Fire Fist
Chance to cast fireball on attack target.
Ice Fist
Chance to cast ice nova on attack target.
Also some armor items for units heroes would be nice.