I find it odd that there isn't already a thread about this. Back on September 13th, a 4chan user (always 4chan, isn't it?) allegedly "leaked" some big details on Super Smash Bros. for Wii U. He stated that by linking your 3DS to your Wii U, you would unlock five characters that aren't in the 3DS version. He claimed that you could unlock Ridley, Chorus Men Conductor, Dixie, Mewtwo, and Impa.

I think that with all the butthurt Ridley fans Sakurai might actually make them shut up, Chorus Men Conductor is so ridiculously off (what with the whole Gematsu thing) that it might be valid, Dixie is highly requested and wouldn't be too hard, Mewtwo is extremely highly requested (almost as much as Ridley), and Impa would be an interesting and fun LoZ character that's been missing from the series. So it could be real, who knows.

But, at the start of the post, he leaked the release date for the Wii U version would be November 21st. Since then it has been confirmed... does that also confirm these characters?

He leaked more, too. The big thing was the Tower of Smash (hence the nickname of the leak). It supposedly will replace event mode (but target test is still returning in its Melee form. Yay!). The Tower of Smash is a tower with 100 floors where each floor has a match with a special challenge/different rules. For example, there are floors that are in slow/fast mode, and one where you're at 300%. You get 4 characters to play as, and every floor ending in 9 has a boss.

Official image - Note that the video linked in the image has one point of NSFW language.

Do you believe it? Do you want to believe it? Personally, though it's hard to say goodbye to Event Mode, I very much want to believe it and I think it could even be true.

Also, something that goes with leaks is the Great Cave Offensive stage that is in Smash U.

It got leaked on nintendos facebook page i think. And got basically confirmed because when you look at the CD in club nintendo it says how one song is great cave offensive

I don't know how to feel about this leak. I mean, the characters part just seems like people stlll butthurt over the Gematsu leak. Still wanting Ridley, after all this?...Really? I mean, he only has 4 attacks, all of those you saw in Brawl, that is ALL he does. And in the older games, he did even less. He just flew, and shot you at an angle to be a jerk. What I'm getting at is, I just don't think he can work as a playable character. Chorus Conductor might be interesting, I can see him sort of like Game and Watch, only utilizing characters from Rhythm Heaven games instead of Game and Watch games. Dixie seems like a pretty solid character, a somewhat mash up of both Kongs we already have. And Impa would be awesome! Unless it's old lady Impa. . Ican see Impa as kind of an Ike clone, if she'll be using her sword from Hyrule Warriors anyway. But as much as I'd like to play as all those characters, I don't think that will happen. But I want to believe it's real. lol
Tower of Smash sounds like fun, I kinda wish that part is real. There better be Porky and Hades as bosses though. (Well Hades or Medusa will be in for sure, Kid Icarus is Sakurai's baby. And we love him for that.) I feel like the WiiU version needs a bit more though, because the 3DS has Smash run, which has the most fun part of adventure mode in it, pummeling baddies from other series'!

On a side note, the Great Cave Offensive is a song on the WiiU version, and Nintendo has given us a few more screenshots of the Kirby stage. At this point, it looks to be either Great Cave Offensive, or Mt. Dedede. Either of those stages I'd love to play though.

Disconfirmed actually quite awhile ago... Here's a list of things he somehow got right:

Transfer custom characters and custom parts
Mewtwo unlocked by connecting 3DS and Wii U
Gaur Plains and Wily Castle being in both versions
There being an extra mode where you have 4 characters to pick, but it has to be different characters. It wasn't Tower of Smash, but he was accurate with you needing 4 separate characters.
Basic modes returning (Classic, All-Star, etc.)
Stage builder way more customizable (surprised he got that correct)

I also hope to God he was also lucky with target tests. Those were so fun!

I think that since there were a few things that he surprisingly got right, the leaker might be a friend of the poster and he just didn't want to give away everything, possibly in fear of getting fired, so he added in some lies. Just a theory, though.