Guess I gotta solve this Ridley debate.....
Argument in favor of a playable Ridley:
1.He is too big in recent Metroid games, but in the original Metroid he was only slightly taller than Samus, so size isn't an issue.
2.The game has even less playable villains than Brawl, with only two antagonists (Bowser and Ganon), one rival (Wario) and one meme (Villager).
3.Since I'm too lazy to write it down

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http://smashboards.com/posts/14609370/
Arguments against a playable Ridey
1.
He's way too big to fit in Smash Doesn't work anymore ^_^
2.The Smash Direct labeled his appearence with "Other boss characters appearences", making him a boss character for the Pyrosphere stage (when Samus fought him in Other: M, which is the game from which Samus and Zero Suit's design in SSB4 is inspired from)
Results: Since shinking down Ridley would still make sense (thank you, NES!!!), the serious lack of playable villains and the lack of counter-arguments that actually make sense (only one), I personally think that Sakurai "will think about it" (see what I did there? ^_^)
Then, I've also seen some arguments about Mewtwo....
So here's mine
1.The PMDT did a playable Mewtwo in 700 hours (or at least that what they said), so it wouldn't be THAT long to make him........
2.He WAS planned for Brawl and was literally almost finished, but was cut near the end for unknown reason and the fans REALLY hated that even though he wasn't good in Melee.
3.The game doesn't have enough playable villains and Mewtwo's a total psycho...... even rarer in Smash......
4.Mewtwo's trophy looks a little weird (those HUGE legs), almost as if it was supposed to be something else before the game's release........
5.If Sakurai wants to make a lot of profits with DLC, Mewtwo will be instantly chosen, because everyone wants it in Smash 4. (Yes, I said IT)