First of all, the Black Knight can only be defeated in chapter 27: Moment of fate. Don't even think of fighting him before that. Before that, your Ike should be 20/20, with preferably maxed Health, Defence and/or Skill. You must have taught him Aether by using an Occult scroll after he promotes, or else the battle becomes impossible. Mist is usable in the battle with the Black Knight, but is in no way neccesary, so you do not have to stress training her. Good luck. You can also escape the duel if things go wrong ________________________________ Fire Emblem Wikifor more info!