This jives well with what NyaseNya and serebii have been saying.
NyaseNya said that Ness would return, and Serebii said that Lucario would get in and replace Mewtwo.
However, if this person is the real deal, then that would mean at least three Star Fox characters in a roster of only 35 (if NyaseNya is to be believed). Remember, Nya said that only the European and North American versions of Brawl would be delayed, so even if Brawl has gone golden, it does not affect the Japanese version.
Taking information from all three of these people here is our roster:
1. Mario
2. Bowser
3. Peach
4. Donkey Kong
5. Diddy Kong
6. Link
7. Zelda/Sheik
8. Ganondorf
9. Toon Link
10. Samus/Zero Suit Samus
11. Captain Falcon
12. Lucas
13. Ness
14. Yoshi
15. Kirby
16. Meta Knight
17. King Dedede
18. Fox
19. Falco
20. Wolf
21. Pikachu
22. Pokemon Trainer
23. Lucario
24. Ike
25. Wario
26. Captain Olimar
27. Ice Climbers
28. Pit
29. Mr. Game & Watch
30. Snake
31. Sonic
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Speculation:
32. Luigi (why would an important and popular character be cut).
33. Jigglypuff (a character since the original, and accidentally confirmed by David Hayter, the voice actor for Snake)
34. A second Fire Emblem character (Marth, Eliwood, or even Micaiah).
35. Either Ray or Isaac, or some sort of WTF final character, or Krystal, (however, why would Star Fox get four characters, tying it with Mario, Zelda, and Pokemon) .
This could be our roster.
However, one of these three (or all three) could be lying. Anyway, these "insiders" will either be disproved or proved in less than four weeks due to Brawl's Japanese release (January 24). However, I would be a tad disapppointed if this did end up being the roster. I will keep a lookout for any new roster leaks or rumors, and will try to notify all the people who don't want to be spoiled, to get off the internet as soon as the leak hits.