What if you were to remove the opponents involvement entirely. If the creature is killed by any source, your creatures gain +1/+1 - +2/+2Targeting it yourself would allow you to activate the ability easier, and I can't imagine that would make it OP.
mitosis, owls eye and crusader / mitosis and flood + water creatures will be a good combo with that card.idk if its OP or not.... good idea though