Okay, here we go. I know I'll get a lot of hate for this, but trust me, I am telling the truth. Anyway, I am best friends with an employee of Namco Bandai and SSB4 developer, who has been telling me some info about SSB4. I've decided to leak it here. First of all, the E3 leak is 100% true.
Little Mac, Pac-Man and the Mii are all characters that are appearing in the game. The Mii can have customizable movesets, but Sakurai balanced it out pretty well with a points system. You have 100 points, and different moves cost a different amount of points. Stronger moves cost more points than weaker ones. There is always 1 free move in each category, so if you run out of points, it's no problem. You can also report offensive Miis during online play. Next, let's move on to Pac-Man.
Pac-Man uses mostly attacks from his arcade game, mixed in with a few moves from the newer games. His main attacks include rolling into enemies, chomping and eating them, and bouncing downwards quickly. He also uses a chain of dots as a tether recovery, and a cherry as an explosive ("Cherry Bomb"). He is currently set to be revealed at E3 2014, although that might change.
Meanwhile, Little Mac has a unique gimmick, Star Collection. The more damage Mac does, the more stars he gets. His Neutral and Up Specials use stars to get stronger. He also borrows moves his enemies use, as well as a zair which uses a boxing glove attached to a chain. Now, let's move on to newcomers you don't know about yet.
As you may be able to tell, Sakurai wants to give most characters a unique gimmick. The 2 other newcomers Sakurai and the team are currently (there will be more) working on shows that. They are Muddy Mole and Zoroark, 2 characters Sakurai found massive potential in. For those who don't know, Muddy Mole is from a retro game called Mole Mania. Muddy's main gimmick is digging. He can dig through the ground by holding down his Down Special. The team is still fixing a few glitches with him, but he's pretty much done.
Meanwhile, Zoroark is the character the team is working on as of now. She will have the Illusion ability, where she disguises herself as another character. If she gets hit, then she will appear normal for a few seconds. Her attacks and hitbox will not change, even if she is disguised as, say, Kirby. It's quite an obvious disguise, but it can sometimes fool people. There are quite a few glitches with her still to work on, so don't expect to see her any time soon.
The uniqueness factor also factors in to other veteran's movesets. Take, for instance, Lucario. He starts out as a Riolu now, and after 20% he becomes a Lucario. After 100%, he evolves into Mega Lucario, who is much stronger. Sadly, since we have both Lucario and Zoroark, this means Mewtwo isn't appearing. Sakurai said that Lucario had a more important role in the games, and decided to not use the anime as a factor of importance this time. Sorry, Mewtwo fans, but just isn't happening.
So, that's all I'll tell you for now, if you have any questions, feel free to ask your questions in the comments! I may not know, but it's worth a try! See you later!