With Masahiro Sakurai's potential departure from the series moving forward, it calls into question who will actually maintain their spots on the rosters of future Super Smash Bros. games.
To the surprise of no one, I'd definitely want to see Ike stick around, both because he's from my favorite video games of all time and because he plays differently enough from the other Fire Emblem representatives. He's also one of the most popular "Lord" characters from the series, so I'd hope that would keep him around.
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As far as new characters are concerned?
I've wanted Shantae to be added to the Smash Bros. roster for years now. Her series originated on the Game Boy Color and eventually branched out onto other platforms and she's gotten more attention over the years. I think she has a lot of moveset potential between her various transformations and also the Pirate's Curse items. I'm glad that she at least made it to the Mii costume stage of acknowledgement, but would prefer her to eventually become an actual member of the roster in her own right. Additionally, there are a few songs from her series that would be cool to have in a Smash Bros. game, particularly some of the various versions of
Burning Town and the
boss battle theme.
Dance Through the Danger would be awesome to have in the game too.
As someone whose favorite Pokémon type is Grass, I'm kind of disappointed that Fire (Charizard, Incineroar) and Water (Greninja) both have fully evolved starters on the roster but the only Grass-type starter is middle evolution Ivysaur. I'd like a fully evolved Grass starter to be added, personal preference toward Decidueye but I'd be open to whatever. Rillaboom would've been cool and I already enivisioned Sakurai doing those screenshot of the day things with Donkey Kong and Rillaboom playing their drums together. I like Meowscarada so I'd be up for them too. Most likely, if they did add one, it'd be from whatever next gen game comes out in the future. But yeah, show Grass some love.
Since Joker from Persona 5 made it into Smash Bros., I'd kind of like to see a representative from the Shin Megami Tensei series since Persona originates from and branched out from SMT years ago. Demi-Fiend from Shin Megami Tensei III: Nocturne might be the most well-known option. The Nahobino from Shin Megami Tensei V is from the most recent and best-selling game, so they're another option.
Considering that we have King of Fighters, Street Fighter and Tekken characters on the Ultimate roster, it would be neat if they would add a Mortal Kombat character for more fighting game representation. Scorpion and/or Sub-Zero are the obvious go-to characters and most likely. I can see why they wouldn't though, with the blood and Fatalities and everything, plus I've heard that MK wasn't ever that big in Japan. They could tone that stuff down and still have suitable Final Smashes without all the blood and guts though. But yeah, it would be cool to see even if it likely won't happen.
Also, considering how much people want him, myself included, it would be cool if they upgraded Waluigi from Assist Trophy to full, playable fighter.