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.
3,034 news items
A day with Pokemon GO Down Under
Splatoon's Last Ever Splatfest is Coming
And It's Sister vs. Sister
Nintendo President Satoru Iwata Passes Away at 55
Rest In Peace
Nintendo has detailed the return of its World Championship
Do you have what it takes?
Disney Infinity 3.0 Edition Officially Revealed
The Force is strong with this one...
Rumor: Disney Infinity 3.0 Leaked Early
Straight from a Galaxy Far, Far Away...
Mario Kart 8 DLC Pack 2...OH YEAAAAH!
Nintendo should do this more.
The Nintendo GameCube: An Interesting Legacy
Will The Wii U Have a Similar Fate?
Project Ukulele - Possible Hint at Characters
Could it be?
Wii's World is not officially affiliated with Nintendo! (but they wish we were).