Alright, with all of this speculation going on, I have decided to make a comprehensive list of every original kingdom hearts character (honestly, there’s no way the Mysterious figure is going to turn out to be a Disney character), and weigh the possibilities of any of them being the Mysterious Figure. Also, I will not include the possibility of time travel in my theories, because if that turns out to be true, then kingdom hearts has crossed the line from convoluted to ridiculously convoluted.
Hayner, Pence, Olette, Sora, Sora’s Heartless, Riku, Riku Replica, namine, xion, kairi, all of organization 13, Lea, Isa Ienzo, All data characters, Xehanort’s Heartless, Terra-Xehanort, Apprentice Xehanort- It is pretty obvious why none of these characters can be the mysterious figure: all of them either didn’t exist at the time or were at a very young age, meaning they don’t have either the build of the MF, or the means to travel to other worlds.
Terra, Aqua, Ven: Once again, very obvious. All three of these characters fought the MF, and have vastly different builds and fighting styles.
Master Xehanort, Master Eraqus, and Vanitus: All three of these characters are single-keyblade wielders, and therefore are unlikely to use duel wielding light-blades. Vanitus is too short, and it would make no sense to have his appear as both the Vanitus Sentiment and the Mysterious Figure. Eraqus and Xehanort also appear as no heart and armor of the master, I doubt either would appear as two different extra bosses. The mysterious figure has a fighting style different from all three, and besides Vanitus it shares no attacks in common.
Dilan, Braig, Auleus, Even: At the time of birth by sleep the doors between worlds weren’t open. Other than Braig, none of these four could access the lanes between, and Braig has absolutely nothing in common with MF in fighting style or weapons or build.
Ansem the Wise: It is apparent that Ansem is a noncombatant, and makes no mention of Terra, Aqua, or Ven in any of his secret reports.
Kairi’s Grandma: WHAT?
So, there you have it. That rules out pretty much everyone in the world of Kingdom Hearts that we know of. So The mysterious figure is almost certainly someone new. Who exactly is the MF then? I have just one guess.
The only person shown to use weapons similar to the MF is Xemnas. As Xemnas is the Nobody of Xehanort (and perhaps, by extension, Terra), Logic dictates that the MF has something to do with Xehanort. I think MF was the body Xehanort originally wished to inhabit, before settling for Terra. Maybe Xehanort had gone from world to world, collecting memories, or something along those lines, from several people, including Vanitus. Then he could have combined them all together, making the MF. This would explain why MF has the abilities of so many others. The ability to use ethereal blades might have come from Xehanort himself. Xehanort’s reason for doing so was to make him a new, perfect body to use as a new vessel. However, things didn’t go as planned, and the MF escaped him, somehow making its way to the land of Departure where he fought Terra, Aqua, and Ventus.
Well, that’s the best explanation I can come up with. Does anyone see any flaws with my reasoning? Anything I left out? Please, tell me how plausible you think it is.