Notes:

Don't get me wrong, it would be neat to have this guy in the game, but there's a 99.999999999999999999999999% chance that this will never happen.

1. He's owned by Square-Enix, and even if they were to include a third-party character, it wouldn't be him because they would probably want to plug Final Fantasy or something instead.
2. Super Mario Bros. already has a ton of reps. There will probably be at least one more for the DLC, but it will likely be a character Nintendo actually owns.
3. Aside from a cameo in Mario & Luigi: Superstar Saga, Geno hasn't been seen in a game for years.