before the level stock up Ike with as many elixers as possible, use none of them before the black knight. the extra units will not atack ike, only mist. retreat mist from the field, then stand near enough to the black knight to be atacked, equip ragnell and wait. the black knight will atack, on your terns heal. evantually you will use aether and wound him badly. you will win unless your ike is low leveled.