Adventure Mode?

[Wes]

Here's an idea.

Basically, the Villain characters will be provided as the "bosses" of each level. In the Mario stage, you'll go through, IDK, Mushroom Kingdom ala Melee. Reaching the Checkpoint will bring you into a fight with Mario and Peach (Luigi replaces one of them if your player character is Mario or Peach). You continue further on, and you reach the Boss Battle. Boss Battle being Bowser in his Koopa Klown Car. Beating this boss will give you a chance to fight to unlock Bowser in the game (Except, we've all decided that Bowser was going to be a starter =/)

These Villain characters will fight differently than the actual fighter battles (You'll end up fighting DK and Diddy normally, while K. Rool will have Canonballs raining down upon you. King Dedede might get possessed by O2, so you gotta knock his HP down to whatever. Ridley called his buddy Kraid to help destroy you.) And through multiple play throughs, you'll eventually unlock the entire cast of villains (If I do believe, Bowser, K.Rool, Ganon, Ridley, Bowser Jr., Dedede, Wolf, Mewtwo, Porky Minch, and ROB (If we count the whole Ancient Minister gig from Brawl)). The other characters, could be unlocked through Classic Mode, minigames, Event Matches (?) and hell, even through Trophy Collection

IDK, platforming overload?

You forgot Wario, Waluigi, Masked Man, Deoxys, and Samurai Goroh.