Yes, I know, the Oblivion is a keychain, not a keyblade, but I just called it that for the sake of simplicity. It's not Ansem's keyblade either, it's Riku's. Ansem wasn't a keyblade master, but Riku was. When Riku allowed Ansem into his body, he gained the ability to use Riku's keyblade which was created from the hearts of the six princesses of hearts. When Sora used it, though, the princesses hearts were freed and the keyblade was destroyed.

I did see the trailer, I didn't really notice the second keyblade in all that flashy motion, though.

I can understand that the blonde haired kid did stuff in the past. It would actually make a lot of sense.

I don't think that you could call the same keyblade more than once. If that was the case, while Riku had the keyblade, Sora should have been able to call it as well, even if his heart was weaker. Obviously, that wasn't the case.

Since they do make mention of a third keyblade, it would make sense that Sora would recieve it. If the blonde haired kid was in the past, he may have been the wielder of both blades previously as well. It would also make sense that he knew of Sora as the future wielder of the keyblade, as Sora is the one who will "open the door to the light."

If he has become an Unknown now, and he was a previous master of said keyblades, it would make sense that he could call them, even if Sora was also their master but at the same time? I think that would get into the title of the secret scenes Another Side, Another Story. Perhaps keyblades exist in different worlds in different forms. Sora's still in the present world, right? Or so it would seem. Well if it's another side, it might be in another world, perhaps the world of darkness. There he might be able to call on another form of the keyblades. I don't know, I'm just throwing out ideas.

I still don't buy into the summoning of the same keyblade more than once (except maybe through the multiple worlds), so the number of keyblades in Deep Dive still don't make much sense to me. Even if that different world thing I mentioned above is true, there were still four keyblades.