Mario- Tanooki Suit, Bee Suit, Frog Suit, Dr Mario, Punch-Out!! ref outfit
Luigi- Mr L, Cloud Suit, Rock Suit, Boomerang Suit, Peach's dress
Bowser- No idea.
Peach- Mario Kart Wii biker gear
Yoshi- Boshi
Donkey Kong- No idea.
Diddy Kong- No idea.
Wario- "Plumber" costume, Dr Wario
Link- Zora Tunic (from TP), Ordon Farmhand/Skyloft Knight-in-Training, LttP Link, Fierce Deity Link, OoT Link
Zelda- OoT Zelda, SS Zelda, Twilight Robes
Sheik- OoT Sheik
Ganondorf- OoT Ganondorf
Toon Link- Outset get-up, Minish Cap(?)
Samus- Completed P.E.D. Suit, Light Suit, Power Suit (a la Prime beginning, flat shoulders), Dark Samus, Fusion Suit
Zero Suit Samus- Other M Fed Outfit, NES leotard (with green hair), Super Metroid ZSS
Fox McCloud- Assault costume
Falco Lombardi- Assault costume
Wolf O'Donnell- Assault costume (unless he already has that, in which case I dunno)
Kirby- Basically any 5 of his various costumes that don't involve radically transforming his body... (it's weird because he'll be losing the hat anyway when he sucks up another character)
King Dedede- No idea.
MetaKnight- No idea.
Pikachu- Raichu, maybe?
Pokemon Trainer- Leaf, Hilbert, Hilda (LOL at those two), Ethan, May
Lucario- Nooooooo idea. Riley's outfit, perhaps?
Jigglypuff- Wigglytuff/Igglybuff? Not sure.
Captain Falcon- Blood Falcon, Phoenix
Ike- No idea, coz I know fuck all about FE
Marth- same again
Lucas- Claus, Masked Man, Pork Army disguise
Ness- robot Ness
Captain Olimar- Louie
Ice Climbers- No idea
Pit- Old-school Pit (less anime, more like his trophy in Melee), Dark Pit
Mr Game and Watch- pretty sure alts for him are impossible
R.O.B.- again, nothing exists for him
AND IF THEY RETURN
Snake- Big Boss, Naked Snake, Old Snake, Tuxedo Snake
Sonic- CLASSIC SONIC