IMO the idea posted by Black/Light is pretty good, there is Midna, you pick her in your selection screen, the game starts you have Midna, all by herself, all the attacks related around her, then when you press vB, you Twilight Summon WL, and ride him, this (IMO) should change your run speed, your jump speed, your jump height (but you would lose the property of your second jump {That is if Midna's second jump would be given a property ir: Gliding or Floating}), your dash attack and your tilts (4 Attacks in total), but every other single attack (Grabs, Throws, Specials, Smashes, Aerials) (18 Attacks in total) would remain either exactly the same or slightly fixed so it won't look weird when riding WL (but not really changing them at all), pressing vB would make WL dissapear and Midna regain her own moveset. This is probably the best idea I've heard