Blaze the Cat
She's nowhere near close to being a front-runner for the Sonic series, and Sega seems content on making her little more then Silver's matyr/sidekick. That said, I loved her in Rush and Rush Adventure, and I'd like seeing her in Smash. I'd even be fine with her as a semi-echo of Sonic.
Henry Hatsworth
A British gentleman from an obscure DS platformer by EA. It was a 'Nintendo Hard' game that combined platforming with (of all things) Panel de Pon style puzzle matching. He wielded a machete as a weapon and could powerful up his projectile weapons by completing the PdP puzzles. It's was seriously way more fun and creative then it had any right to be. It wound up flying under the radar because EA in all their wisdom marketed it as a shovelware game.
Dracovish
A Pokemon who isn't cute, heroic or legendary pretty much has no chance of making the cut. Nonetheless, I would love to see the giant mutant fishie with the funny move in Smash. Having no fists, it would have to relay on it's kicking and biting attacks, and it would be both hilarious and awesome.
Popeye
Hey you said impossible choices. I don't know how many of you have watched Popeye cartoons, but this is one of the most badass cartoon characters in history. Some films have him doing fights that you'd swear you'd see out of an anime or something, I've even heard his crazy style was an inspiration for Luffy from One Piece. In addition, Popeye is also inadvertently responsible for the creation of Donkey Kong and Mario since Nintendo at the time couldn't get the rights to do a Popeye game. Naturally his final smash would be to pull out a can of spinach and wail on the enemy as his theme plays.