I played some of this with some of the other KC players and maybe took is slightly seriously. Take the feedback in that regard.
As a whole game, it's pretty fun. Most of the characters seem broken enough to compete, a few exceptions I'll bring up. If we were going to take this game seriously as a tournament game (shocking I know), I think the main problem it would have would not be any one character dominating but rather that there exist a wide number of hard counter matchups. I don't know how much those bother this development team, but I think in the long run most people would either use several characters with Zelda & Sheik, Pokemon Trainer, and Samus having the benefit of option select character picking.
Specific character feedback:
Bowser is the most polarizing character by far. Low damage "combo" characters have almost no hope of beating him. Some characters have a few good options to pierce his armor and have evenish matchups. The other heavy hitters just wreck him, and he has no hope of winning. In specific, I saw that Bowser beats Lucario at least 80:20, goes close to even with Pikachu probably slightly Bowser's favor, and loses to Ganondorf at least 10:90 maybe even worse with severely uphill matchups against Ike and Captain Falcon as well but better against them than against Ganondorf. Bowser is beyond unviable as a main, but he makes a ridiculous secondary. I'm not sure if Bowser is fixable given his current design, but I think at a tournament level Bowser would be the single biggest problem for the metagame. I don't think he even would earn a tier placing because of this status...
Olimar is super bad and as far as I could tell easily the worst character in the game; you guys really just need to rethink him. Olimar feels nerfed from standard Brawl which given the power level of the game is a really, really bad sign for him. The small thing is a nice thought in a way, but it really does hurt him more than it helps him so if you want to run with it you should tweak his physical attributes a lot to compensate. He also needs something better than a buffed Pikmin Pluck which is honestly barely useful.
I spent most of my time using Pokemon Trainer for his flexibility in working around hard counter matchups, and I mostly liked what I saw (if I play more Brawl-, it will be as a PT main). You guys mostly did a really good job on Squirtle, but a small tweak that could be fun would be increasing the speed boost he gets from turning around (one of the earlier listed physical attributes governs this) to make his pivot gimmicks even better. Ivysaur feels like he needs a little help, but he's close to right with a mostly good feeling and the hilariously awesome bair. I really don't like the feel of his recovery very much, and I'd kinda like dsmash to have a little more bkb to be more reliable at the game's power level. Dunno if you guys did anything to Razor Leaf and Bullet Seed, but both were getting some good mileage for me even if they were kinda tricky; small buffs to either move are another possible way to make Ivysaur just make that small leap he needs to be just right. Charizard, however, feels really underpowered. I didn't explore him much because honestly he seemed pretty bad, but I think he needs some attention and love for your next release (buffed Rock Smash! You know you want to!). I can't even say anything more about Charizard because I wasn't doing much other than getting smacked around and wishing I had awesome stuff like everyone else whenever I was him.
I also really, really dislike the removal of auto-switch. If I'm actually playing as the trainer, isn't that a sign I actually want to use Squirtle, Ivysaur, and Charizard? I was actually switching at the start of stocks even unsafely just because not switching as PT was really annoying me and was making it hard for me to use the character the way the character is fun for me (which involves a constant mix-up of playstyle by shifting character).
I also don't know if you guys included all the costume files for PT on the SD card (I was a little... overwhelmed by other factors to notice my switch time), but if you didn't, you really should and also make sure the animations involved with switching go nice and fast. I am mostly saying this to make sure it's known that not everyone subscribes to the insanity of solo Pokemon, and some of us really like PT himself! All around, PT is probably near the top of the 2nd tier right now, mostly not top tier because Ivysaur is slightly underpowered (not too bad) and Charizard's main role on the team is slowing down your ability to switch from Ivysaur to Squirtle...
Other general tier comments...
Ganondorf, Ike, Zelda & Sheik, and Ice Climbers are just all around really good, probably top tier. Even among the game's generally broken characters, these guys really stand out. Zelda & Sheik is my pick for the best character in the game, probably with a heavier focus on Zelda but Sheik has some silly stuff too so you can't rule her out as an important character half. All around, all these characters are also fun to use and fun to fight against so I'm not saying this as a suggestion to nerf them so much as just trying to identify them as top tiers.
Pikachu, Jigglypuff, and Captain Falcon are safely high tier but probably not top. Most of the rest of the cast is hard to place so if I don't mention them later, it doesn't mean I didn't use them it just means I'm not sure of how good they are yet.
Snake and R.O.B. are single change gimmicks that are probably very powerful and would be big factors in the metagame. It's hard to say how they'd play out, but I don't like how they work out relative to the formerly listed top tiers (who are top tier because they have a ton of broken stuff, as opposed to one thing that's really, really broken and then the rest of them is only kinda of broken).
Ness and Mr. Game & Watch feel underdone and underpowered. I've already chatted with Linkshot a bit about G&W, feel more strongly about that having used him more. Ness is just... underwhelming in every way. He's not awful, but his power level and flashiness are just way below the standards of this project. He needs serious attention for your next release, but I have no suggestions.
That's all I have; I hope it's helpful. God job on making a fun game with a lot of identity. I hope you guys decide to take the effort to actually tweak for balance while not lowering the game's power level and give some attention to a few characters who IMO kinda fell through the cracks; I wouldn't mind seeing a honed version of this as a routine side-event at tournaments.