Keep in mind that this is a rumor before running with it!
Super Smash Bros. Ultimate sure seems to be living up to its name, with over 60 characters announced for it so far, including every single character from every previous game in the series, as well as some new ones. However, in spite of series creator and director Masahiro Sakurai’s earlier insistence that there are not many characters left to reveal, and they will have to slow down with the pace of announcing them, it seems like there may still be quite a bit to come.
An alleged—alleged, mind you, as in unconfirmed, so don’t take this as gospel—bit of marketing material for Super Smash Bros. Ultimate has emerged in leaks online, collated in one place at ResetEra.
The unannounced characters for the game, according to this leak, are Shadow the Hedgehog (potentially an Echo), Isaac (from Golden Sun), Ken, Mach Rider, Geno, the Chorus Kids, and Banjo-Kazooie. That last one could be a major megaton announcement, since it is effectively a first party character for a competitor included in the game, even though it has a history of association with Nintendo.
As said already—this leak may not be genuine. We will know either way once the game is out, or these characters are officially announced. Super Smash Bros. Ultimate launches for Nintendo Switch on December 7.