KIRBY!
I didn't even think about Kirby! Good lord, I think this could be the beginning of a D&D version of Super Smash Brothers...
Link: Gish.
Mario: Leap Attacking Gish.
Ike: Shock Trooper Power Attacking BEAST.
Diddy & Donkey Kong: Anthropomorphic Simian Master Throwers. Donkey Kong has Brutal Throw.
Ness: Psion of some sort. Given the PSI powers in the games, I'm guessing a Kineticist or Egoist.
R.O.B.: Warforged Warforged.
Solid Snake: Any rogue with HIPS and Darkstalker and a tricked out Hide and Move Silently, otherwise the box-hump wouldn't work.
Sonic: Chuck E. Cheese on an Anthropomorphic Hedgehog.
Only ones I can think of at the moment.