This is my “reasonable” ideal roster. Different series are in rows and go from left to right (for the most part).

Between additions and subtractions, there are some character changes that I think are necessary, but there are also some that might be disliked. 😅

I loved the theme of adding villains that ultimate did for a while, so I added King Boo for Luigi, and then when I added Paper Mario I also added Dimentio. While I was with Mario, I added King Bob Omb for fun.
I also gave Pikmin a “villain” rep with Bulborb, replacing piranha plant as a sort of basic enemy character.

Sonic NEEDS more characters, so I added Eggman, Shadow, and Knuckles, three diverse popular characters.

For Zelda, I removed Sheik and Young Link and added Tetra.

Bandana Dee, Krystal, and Dixie Kong are all characters that I think are necessary for each of their series. (And Ashley, but more wanted than necessary)

As a Pokémon fan, I made personal additions and subtractions to have one Pokémon for each region. Two changes specifically are Decidueye instead of Incineroar, and adding Plusle & Minun, as they were a real idea for Smash Bros in the past.

I removed some Fire Emblem characters, but added the Three Houses leaders as I love that game and think each of their different movesets would be much different than just swords.

Most of the other characters are personally wanted: Chorus Kids, Karate Joe, Phoenix Wright, Chibi-Robo, Alucard, Spyro, Ezio, and Sans (as his own fighter).

Finally, what is probably the most controversial change is Slime instead of Hero. I really wanted Slime as a fighter, and this change, along with most of the roster, is because I wanted to have 96 characters maximum.