here are my thoughts.....

may be sum chars like:

Knuckes (same atks w/ some diff. here and ther; could be slower)
Tails (similrar atks, but weaker and he could fly)
Birdo (a yoshi mirror)
WaLuigi ( well we got wario didn't we?)
Paper Mario (we had Dr. mario once so why not)
Bowser Jr. (smaller and faster bowser mirror)
a fighting PKM (ex: Blazeakin, Hitmonlee, hitmonchan, Infenape, etc)
YOUR Mii!
Raichu (pika mirror but slower and stronger)
meowth (replace that damn jigglypuff!)

may be some chars that were played on nintendo platforms:
Megaman (Samus mirror)
Zero (well idk what he'll be like but theres a thought)
Custom RObo
and a final crazy one:
NARUTO! (we got snake from konami so why not naruto& co., id buy it :D)

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