Piranha Plant - Should've been base roster, personally would've went with Paper Mario or Waluigi or Geno if you want to take from Mario franchise so badly
Joker - Definitely a UNEXPECTED HUH WOW pick and it worked AMAZINGLY WELL, I could see arguments for this one
Hero - Honestly shouldn't have taken this long for DQ to be represented in a Nintendo Franchise like this, also unique mechanic
Banjo - Already said my thoughts
Terry - You can tell that THIS was Sakurai's personal pick from how he spoke about the character/franchise with passion, let the man put his dream character(s) in the game, not dissing on KoF or saying it doesnt belong mind you, not to mention unique mechanic
Byleth - I got nothing for this one, going to assume he was throwing JPN fans a bone like he did Banjo for US fans, if so thats fair
Min Min - Unique Playstyle/Concept, plus ARMS and Xeno 2 was originally planned to be in the game anyway, deserved spot
Steve - Extremely unique, from a well known franchise, most likely a business deal but it is what it is, what do i know
Sephiroth - Iconic Villains are ALWAYS welcomed, ESPECIALLY ones that aren't bullshitting around on some not goofy shit (see Ridley)
Pyra/Mythra - See Min Min
Kazuya - Villain (great!), We already got literally the other main fighting games in the series, why not, also a UNEXPECTED HUH WOW pick tbh
Sora - Deserved, no i will not elaborate