Oh my gosh, I have so many! Here goes...
Meowth: I'm probably biased because cats and Pokemon are my two favorite things, but he'd be a great rep imo. I love the thought of him being a fast, scrappy little fighter with good range on his claw attacks and Pay Day covering a lot of space in much the same way it currently does.
Alternatively, Team Rocket: It might be a little weird to include Jessie and James when they're primarily anime characters, but they've at least had game appearances and would be a fun take on a different type of Pokemon Trainer. Like Squirtle, Meowth is the small-and-fast one, playing the same as he would solo except he lacks a down B, since that's Pokemon Switch. Then you include a character who can stack up to the power of Charizard. I'm not quite sure who, but Weezing with Explosion comes to mind. Another good choice would be Victreebel, since James has a thorny Pokemon tormenting him every other generation or so, and Victreebel is probably the most well-known. But, instead of an Ivysaur equivalent (I see Victreebel as more of a slow powerhouse like Zard, though could even function as something of a hybrid between the two), we would have... Wobbuffet. This would be a weird af fighter who couldn't do much but whose moveset is entirely based around counters and reflectors.
Gengar: Gengar is either my second or third favorite Pokemon, depending on how you look at things (Umbreon and Incineroar tie for my favorite). I really want a ghost in Smash who has ghost properties, like y'know, phasing through stuff. I could see Gengar have an attack that lets it phase through the floor to help it close in on foes, and I think a passive ability where it auto-phases through attacks would be really cool, rendering the character hard, if not impossible, to true combo. If you delay your follow-up to wait out the phase, though, your combos could seem true, as I'd imagine Gengar would have subpar frame data to help balance this out. Additionally, Gengar should be very lightweight, so that it does not take too many well-timed hits to take it out. A phase-out that auto-dodges attacks would be overpowered otherwise.
Eevee: Eevee is my next favorite after Gengar, and well, I'd want it to be perhaps the most ambitious fighter yet! You could of course just have Eevee on its own as a quick, scrappy fighter but of course, I'd rather see the Eeveelutions. You could have it where you can only evolve once per stock, or have it where Eevee is a mutant who can evolve and devolve at will. The latter wouldn't be very canon, but would be more fun and interesting. Each Eeveelution would obviously play differently, but for the sake of preventing this book of a post from reaching Biblical lengths, I won't go into how I think each would work. But yes, this does also stem from me loving Umbreon and wanting to play as it, but not wanting to only have Umbreon so that the other Eeveelutions get the spotlight too!
Mew: I've always loved Mewtwo's kit, but Mewtwo definitely suffers a lot from being so big, light, and floaty. Enter Mew, a semiclone who solves the size problem and could maybe also be more of a fastfaller (doesn't have to be a fastfaller full-stop, just less floaty). Mew would have a slightly better combo game, but less range and kill power (though I'd like for the throws to only kill a little later). Mew would be the safer pick of the two, while Mewtwo would be the more powerful one. I think it would make for a really neat dynamic! (Also, Mew can't learn Disable, so maybe it could have a unique down special.)
I'm not the biggest fan of generation 2 only being repped by "worse Pikachu". I like Pichu alright and all, but regardless of how anyone feels about it, it was intentionally designed to be an inferior version of an existing character. And to have my favorite generation repped in that way honestly stings. I do like that it also reps Baby Pokemon which were new at the time, but Pichu would sit a lot better with me if we had another gen 2 rep who wasn't a joke character. So...
Scizor: I think this would be the ideal gen 2 Pokemon to add, especially back in Melee. It reps the new evolutions of gen 1 Pokemon, in addition to repping the new Steel type. Steelix and Umbreon would also rep new evolutions and the new types, but would probably have been more difficult to implement back in Smash's infancy. Yes, I am wanting Celebi to take me back in time and somehow adding Scizor to Melee here. It also helps that this Pokemon has aged very well, remaining a favorite of many fans.
Tyranitar: Quite possibly the most beloved gen 2 Pokemon, I think this would have been a great alternative choice to Scizor. It would be a slow superheavy with a few Rock-type attacks which would offer it good range and power! And I just think Rock would be a really cool type to have in Smash, because we have like no Rock-based attacks other than Zard's Rock Smash, which might be gone forever, and Kirby's Stone.
Grovyle or Sceptile: Like many others, I want a solo Grass starter, since we have Greninja for solo Water and Incin for solo Fire. Either of these two would be my #1 choice, with Grovyle there for the PMD references.
Blaziken: So, here's a weird idea. I feel like Blaziken would be a really easy character to add as a composite character. You could Frankenstein it together with moves from Captain Falcon, Charizard, Ryu/Ken, and Incineroar. It honestly wouldn't need a single original move, though I'd love for its down special to be Rock Smash so that we can retain that move if Charizard will never have it back. Who knows, maybe there will be another Fire Pokemon in the future who I'll feel this could be done with, and maybe they will? Maybe it's just that I love fire moves and love the power these characters bring, and having a composite of them sounds really fun to me. It wouldn't have command inputs or auto-turnaround from Ryu/Ken, I just see it potentially borrowing some of their aerials and/or tilts, averaging out the power of them between the vanilla and command input versions.
Gardevoir: This Pokemon would probably feel very elegant and smooth to play as, and is a fan favorite who I think would work great. You wanna know the funny thing about Mewtwo? It doesn't really use Psychic power much, instead opting for a shadowy moveset. That's probably because it's meant to be the "villain" for Pokemon. But it doesn't feel like we have a very Psychic-centric user, which could be fixed with Mew (just give it pink effects on everything except Shadow Ball), but also could be fixed with Gardevoir. I see its main gimmick being a shield of some sort, much like the Pokeball summon. Perhaps you could have it so that it has a second shield for its down special, like a better Pit Orbitars, or perhaps its regular shield could heal it in very slight amounts.
Garchomp/Cynthia: Gen 4 doesn't really need anyone other than Lucario, but I think Garchomp is bad*** enough, and enough of a fan favorite, to be the Pokemon I would want most from gen 4. Something I like even more, though, is Cynthia as a type of Pokemon Trainer, with Garchomp as her powerhouse Pokemon. We don't really have any representation of the Champions, unless you count Red and Leaf, but their Smash appearance doesn't say one way or another if they've become Champion yet. I think either Togepi or Togekiss, and Spiritomb, should be Cynthia's other two Pokemon, since she gives you the Togepi egg and always includes Spiritomb on her teams, usually leading with it.
Zoroark: Probably the ideal gen 5 rep, I like the thought of it being a Lucario echo without Aura. Its range and power would be averaged out, perhaps even better range overall because it could have claw attacks (think Wolf). I'd also like it if it was a fast faller to contrast Lucario's floatyness. (I'll admit I prefer fastfallers, but I also think it makes for an interesting way to differentiate fighters that probably wouldn't take much work to implement.)
Genesect: This would be awesome, and a great alternative Bug/Steel type to Scizor! I love the thought of it getting in and having its rivalry with Mewtwo, and there's a lot you could do with the drives and Techno Blast (maybe a stance change like Shulk but instead gives it a different neutral special) and it turning into that weird UFO flight form, it would just be a ton of fun!
Hawlucha: Honestly Greninja is the perfect gen 6 rep and we don't need more, but I may as well shout out my favorite Fighting type! Could be an acrobatic and nimble wrestler to contrast with Incineroar's slow take on wrestling.
Decidueye: Another option for a ghost, though I doubt it'd have the phase-out thing I want and would probably play more straightforward. I love Decidueye, as it's my Pokken main and would have been one of my Smash mains had it been chosen over Incineroar. I'm happier with Incineroar, but still, I can't help but kinda want Decidueye knowing it almost made it in.
Mimikyu: My final choice for a Ghost-type, this probably also wouldn't have the phasing thing but would be very neat nonetheless, being a small, speedy grappler whose gimmicks would probably revolve around bringing its foes under its cloak, and Disguise could maybe have it take less damage up to a certain %. My favorite Fairy type!
Rillaboom: My favorite Grass starter! I think Rillaboom would be super fun, probably heavy but speedy like DK. It'd be more based on using its drum, though, which would have a lot of range and power.
Toxtricity: My favorite Poison type, I think it would make for a really fun and unique fighter using its electric guitar (literally made of electricity!) and poison, which could perhaps let it do damage over time.
Obstagoon: Kind of an underrated pick in terms of gen 8 reps, but I absolutely love Obstagoon and love its gimmick of using Obstruct, which I think would translate pretty well to Smash: have it be a counter, but it doesn't do what counters usually do and instead, doubles the knockback of Obstagoon's moves for 15 seconds.
And I think that's every Pokemon I want, thank you for coming to my Teddiursa Talk!
