Just a shot in the dark, but I propose that if Dr. Mario isn't going to appear in the game, he should at least be commemorated by a Card. Same goes for any other characters not returning from SSBM or SSBB.
I've got a fairly comprehensive knowledge of the Mario series, and I can't say there's anyone else important that you're missing.
I've got a fairly comprehensive knowledge of the Mario series, and I can't say there's anyone else important that you're missing.