They were seen holding the letter that Mickey sent to Sora at the end of the KH2 epilogue. Apparently this game is a link between KH2 and KH3. I'd call it a main entry, and not a spinoff. And looking at the HUD and battle system...looks legit to me
Edit: It's always the *secret* ending that leads to the next main entry in the game. The basic ending after credits always has led to a spinoff. In KH1, the basic ending showed Sora waking up on a road where Pluto runs away. The secret ending was Riku in clothed garb fighting heartless at the World That Never Was. As we know, the "road" ending led to Chain of Memories, while the Riku fighting ending led to KH2.
In KH2, the basic ending was the message in a bottle. The secret ending was the Keyblade Masters. This leads me to believe that KH 3D is the result of this basic ending, thus being the spinoff, because the secret ending led to Birth by Sleep. Not to mention that BBS got a Final Mix (something only the main entries get). Whatever the basic ending of BBS is will be the next spinoff (if there is one) and the secret ending will allude to the next game. Unless the secret ending is similar to the message in a bottle ending in KH2, in which case KH 3D will be the next main entry.
Seems like a reasonable observation, right?
