As for my character rankings, I'm gonna exclude Sora for now because that's yet to be seen. Like I said before though I'm pretty impressed with how he looks despite not liking the character choice very much so he's lingering somewhere around B tier for now.
S TIER:
Just straight up, the fact that K. Rool and Ridley are in this game still astounds me and stand as the most satisfying reveals in my experience speculating this series. K. Rool is absolutely FLAWLESS - literally best case scenario and more - and while I have my reservations about Ridley's overall design, the effort is there and I still find him to be a whole lot of fun.
Meanwhile, Terry is just so cool. He's not a character I rooted for, and I don't have much stake in his games either, but damn the amount of love poured into this character is infectious and his redemption from "literally who" for most of the community into a near unanimously embraced part of the Smash family is something truly special. In my opinion, those kind of characters are the best.
A TIER:
There are a whole lot of different reasons that I like these guys. Banjo and Sephiroth are just fantastic additions that are both fun to play and made tons of people happy, which made me happy. Meanwhile Incineroar and Plant are some of the most pleasant surprises in Ultimate, despite being skeptical at first I quickly fell in love with their charisma and creativity. They're so expressive and fun, definitely among my favorites to play in the game.
Simon and Hero are great celebrations of series that honestly feel like they always should have been here. I like Simon's design a little better just by nature of not being super into crazy gimmicks, but Hero is easy to love for the sheer chaos and laughs that they bring along with them. And Steve? Honestly, Steve is the MVP of FP2 for me. I was never a big Minecraft guy but man, I love oddball characters and I sincerely appreciate the variety that Steve brings to the table. There's nobody else who plays like him and nobody else who could.
B TIER:
I love that Isabelle and Min Min are here a whole lot, I'm just critical of their implementation. Isabelle remains a bit too similar to Villager for my liking, and although some of her new tools are very cool... I don't think she got the proper amount of love she deserved, it almost feels like they sorta gave up halfway. But I really do love Isabelle. And I think Min Min is awesome, but man they did make her frustrating to fight against. Implementing a disarming mechanic would have went a long way I think, it wouldn't have felt too out of place either since that's such a prominent part of ARMS gameplay anyway.
Kazuya and Inkling are rock solid additions, I'm just neutral toward them! I think they faithfully represent what is special about their series and introduce some fun gameplay ideas, they just haven't knocked me out of the park the same way a lot of the other guys did yknow?
C TIER:
Generally a bit more underwhelming for me. I hate to say this about Joker, but I dunno I think I like everything ELSE about Joker's inclusion (stage, music) more than the character himself. He's kind of plain, which is fine but I'm just not big on the meter / comeback stuff. And then Pythra is alright, I think they're a good take on the tag team mechanic, but in retrospect just aren't really anything special for me. I think they have some cool moveset ideas but that's counteracted a bit by how frustrating some of those ideas are to deal with. No disrespect toward these two, just not up to par for me.
D TIER:
I'm not special for saying it, I just don't like Byleth's inclusion. I think they also have a pretty fun moveset, and honestly I'd like to give them another go and hope I'll come around on them some more. But I mean, I think Corrin is fun too. I just don't think either of them were good additions. Power to you if you like them though! Kind of pointless to be holding grudges toward these guys anymore though, let's just enjoy the rest of the roster right?
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Overall, I think Ultimate has definitely delivered on that name. Some of the most highly requested characters ever have joined the roster, from beloved first parties to pipe dream third parties and a ton of welcome surprises in between. I wish there was a little more variety across the DLC here and there - over-reliance on stuff like comeback mechanics and catering more to certain audiences, I would have especially enjoyed another Terry esque surprise pick too - but all in all it's hard to complain with such a diverse and fun roster of gaming icons. I think my overwhelmingly positive ratings of the roster speak for itself.