Ulti idea

So i had this idea for an ulti a champion could have that would allow friendly fire during teamfights. For example AOE skills would affect your teammates as well as the enemy team. Or skillshots that pass through units, like Varus' piercing arrow, would do damage to your teammates also if they passed through them. It could last for a few seconds and i think it could really be a game changing Ulti to have and also very trollish )))