I'll list what alternate costumes I think characters should have
Link+Mario, same as cervy
Samus
Zero Suit Samus
Phazon Suit Samus
X-Samus(from Metroid Zero Mission or Fusion for Gba, either way the blue one)
Dark Samus
Pokemon Trainer
D/P Trainer, M/F
G/S/C Trainer M/F
R/S/E Trainer M/F
Fr/Lg Trainer F
and each generation different trainer should have different starters.
I'll post more later
Credit to .Impact for the sig & avy