Long post ahead.
I know this has probably been brought up already, back a while ago, but I want to point a few things out.
First of all, I strongly believe that Mewtwo will return. That hasn't changed for a while, and the factors for it just keep building over time.
Mew is a confirmed pokeball. You can see her in the trailer. I know this doesn't have as much relevancy considering Mew was a pokeball in Brawl and Mewtwo was a trophy, ;__; but this will be the 3rd time that Mew has returned as a pokeball in the game, so it's a running thing. Look at all the newer pokemon that are out (there's what, over 600 now?) but they are STILL including the old school Pokemon like Mew and Charizard.
As for the Greninja reveal, I believe it was animated that way on purpose. How many people believed it was Mewtwo when they first saw the trailer? LOTS. I didn't think it was Mewtwo, but this wasn't the case for a lot of other people. Look at all the reaction videos on YouTube and the number of people that say they were fooled at first. It was intentional by far because out of all the other ways they could have introduced Greninja to us, that was the way they decided to do it. I don't really buy the whole 'ninja in the shadows' thing because despite being a ninja, Greninja is a frog. Why not animate some super awesome water fight sequence or something? Instead, we see him hanging upside down from a tree, charging up a water shuriken. It resembled Mewtwo in basically every way so no wonder people were fooled. They made it look as epic as possible to make people believe they were seeing something they weren't really seeing, if that makes sense. The webbing in his fingers isn't even there from what I saw, nor is it blacked out by shadow. Because if it is there, it would need to be really far down. Look here, it's right up near the tips
Compared to this? It's gone entirely! And his fingers are nowhere near as rounded as they are in the above picture.
Would you think this was Mewtwo on first glimpse? (I know it's silly for him to hang upside down, but the silhouette is a different story.)
Maybe not, but you have to admit it does look like him there. Greninja's horns look like his ears and his tongue looks kinda like his tail.
Everything we see is clearly intentional. They put thought into this trailer.
Mewtwo will return. Sakurai knows the demand. This has been brought up numerous times before, but remember he didn't
have to call out from the audience with 'We're thinking about it!' but he did. Something prompted him to. Mewtwo was
only cut from Brawl because of time constraints and the fact his model was glitching out with the SSE. And on top of that, look at all the promotion for Mega Mewtwo Y. She just ups the chances of either Mewtwo getting into the game. We could even get Mega Mewtwo X.
Come on guys. What more evidence is left, apart from the huge list of positive factors that see to Mewtwo's (male or female) return? They've been saving his reveal till very last or as an unlockable
or even DLC like he was in Melee. If we don't hear anything even when the game is released we will only have to wait a few hours until people that play it confirm whether or not he's in. And look at Brawl. There were 3 or 4 characters or something that weren't even revealed, they were just found in the game.
There are just too many things going for Mewtwo to not be in Sm4sh. I couldn't fathom why he
wouldn't return at this point, but if he doesn't I'll be pretty damn devastated.