This is kind of speculative at this point, but a video that was available in the Japanese section of the official Super Smash Bros. Brawl website apparently revealed three characters early, as found out by a GameFAQs poster called Edible.
As we know, some stickers can only be applied to certain characters. On selecting one of these stickers, small icons of characters appear in the bottom corner of the screen. It's a little hard to make out, but snaps taken from the video indicate the presence of Lucario, Ness and Jigglypuff.
Lucario and Jigglypuff?
The video on the Dojo has since been edited by Nintendo, but the original has been uploaded to YouTube and can be seen here. The small icons appear around the 4:20 mark.
Make of it what you will.
3,021 news items
Yacht Club Games Interview
David D'Angelo gives us some chat on Shovel Knight
Reggie Fils-Aime Talks Nintendo Third Party Woes
Who needs Call of Duty when you have Mario and Zelda
11.5.2014 Nintendo Direct Showcases Upcoming Games
2015 shaping up to be a great year
Nintendo Introducing a Pre-Download Option for its Digital Releases
An exciting idea that brings a potential problem with it
Former Factor 5 President Reveals Cancelled Rogue Squadron Game for the Wii
The force wasn't strong with this one
3DS Homebrew Channel Back on Track After Slight Delay
Giving gamers a place to brew their own games
Pokemon: Omega Ruby/Alpha Sapphire Dual Pack Confirmed
Why choose, when you can have both
Wii U Owners Frustrated Over Low Stock for Bayonetta 2
This witch is proving elusive for gamers
Super Smash Bros. Overload
8 player smash, new game modes, stage builder, and the return of Mewtwo
Wii's World is not officially affiliated with Nintendo! (but they wish we were).