Also, it decreases the chances of clones. I don't want to have any clones this time ... SSBM had far too many.
Mario -> Doctor Mario -> Luigi
Captain Falcon -> Gannondorf
Pikachu -> Pichu
Marth -> Roy
Fox McCloud -> Falco Lombardi
Link -> Young Link
Hopefully, some of them are to be dropped, and others revamped seriously.
My take:
Doc Mario should be cut, and Mario and Luigi should have seperate moves influence by their GC games (e.g. FLUDD and Poltergust 3000). Captain Falcon might stay, but this means Gannondorf needs some serious work - he's had loads of unique stuff since the days of Ocarina of Time (e.g. double sword combo, ball of black magic, morph into Ganon). Older Pokemon could possibly be cut out in favour of newer ones but not really sure. As for the Fire Emblem duo, Roy will probably go for his over-power, and Marth will need a brand new moveset. In terms of the Star Fox pair, Falco is pointless and can be dropped, while Fox can just get an update. Finally, Link should be Twilight Princess style and Young Link should be Wind Waker style - movesets can be the different items from the two ages in Ocarina.