King K. Rool is pretty popular among fans, and was considered to be in the "Unholy Trinity" of heavily requested characters (him, Ridley, and Mewtwo) prior to SSB4's release. He's doing quite well in the Smash Ballot from what I understand, so it wouldn't really surprise me if he was added.

As for this leak, let me know when people finally learn how to take screenshots, or at least decent photos.

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