Whilst I'm not sure about there being too many third-party characters, I'd absolutely love to see Spyro or Crash (particularly Spyro) added to the roster because they're classic gaming icons, even if they went through rough periods.

Out of all of the new Pokémon, I'd like either Sceptile or Decidueye; both are Grass-type starters, which would mean a starter of each type would be playable, and I think those two in particular have a lot of possible moves that would lend themselves very easily to a fighting game. A not fully evolved Pokémon would be nice too, if only for a little bit of representation. Something like Salandit, perhaps.

Kirby and Zelda definitely need some new characters, so I'd like to see Magolor and Impa added too, because I feel they would work particularly well and have some interesting moves. Bandana Waddle Dee would be an alternate choice for Kirby, as it seems to have become a recurring character in recent years. A Revali skin for Falco, while unlikely, would be a nice reference too.