Geno (From Super Mario RPG:Legend of the Seven Stars) was actually supposed to be in Brawl. There is a beta form of him still stored inside of the game, but it's only accessible through major hacking. I just thought everyone would like to know this.
And the reason he wasn't in Brawl is because SquareEnix (The creators of Final Fantasy) worked with Nintendo on Super Mario RPG, but they said no to Geno being in Brawl for some reason, and since they worked on the game, Geno is partially theirs. So they have a say on what games Geno can be in.