Oh boy, this ones a toughy.
Now if it were up to me, I wouldn't cut any character in the roster knowing everyone has had a significant impact on the series & it wouldn't be fair to the fans of those characters. However, this topic isn't about that, it's about clearing for more memory. So here' what I would choose if you were to put a gun to my head on deciding on the cuts for the roster.
Being original & not pick any clones or miis:
: Not because she's high on the "tier list" or any of that crap, it's mainly because she's really become more of a Smash Bros character rather than a Zelda character, since she really doesn't represent any of the games other than OoT.
: If Metroid were to receive a new character aside from Samus, I would be fine if ZSS didn't return. Doesn't mean I hate her though.
: Aside from the Aura mechanic, I really haven't seen the appeal towards Lucario, onces again it doesn't mean I hate him, I just think he doesn't do much even if he's representing Gen 4.
: Same story with Lucario, only with Gen 6.
: I'm sorry Jr, I love your concept, moveset & alts. But if I were to see any of the Mario characters that would get the boot, it would be you. Rosalina, it just doesn't seem like she's going anywhere.
As for the newcomers, though I would love to put character from already existing franchises, I think other series need some more love.
I would go with either Mach Rider, Saki, or Isacc.
