yes what he did is a mystery but the story in a whole is not all that mysterious. hear me out. i mean everything is not a mystery to him. he pretty much knows everything that's going on. he knows that Ansem SoD was a fraud, he went after the Kingdom Key D, he knows mostly everything and he feeds the info to Riku and Sora...playing a character that knows a lot takes out the discovery element. I mean in KH1 we had to found out who Ansem was, KH2 Xehanort was, Days what Xion was all about and Roxas' adventures, and BBS TVA fate, a mickey game? what is there to discover how he got the Kingdom Key D? What he saw in the Realm of Darkness? idk and i wouldn't feel too comfortable playing as mickey...it was a bit of a nightmare controlling him for me...he was way to small, but kickass. a party member sure, a side scenario why not? but a whole full fledged game is not something i'd want.