There is only one way to redeem this form. It will show up randomly as you change into forms. Lets just say you wanted to form into Master from one day, when you were forming, you notice that Sora is white. You have unlocked Final Form. It will take a while. So train for it!

You are right, but also wrong. It will happen randomly, but only after a certain event (won't say, because I don't want to spoil it for others) in The World That Never Was.

oh yeah, that's right, after the battle with ---------(Spoiler)