Every time I end up using Squirtle, I get sad.
We sowwie Reflex!
Someone ought to use him at the least. Like Day one and pre-release Squirtle looked to have all this potential with giant bubble RAR spacing and Sonic-level noncommitted approaches, but trying it out first hand and most anecdotal evidence seems to indicate he's super open to anything on whiff and that his obtusely large SH is a severe detriment. He's possibly the only character baring maybe Zelda that can't empty SH grab.
Tying this in to my thoughts, Squirtle has a very hard time approaching certain short characters, because you have to fall with aerials to hit them. Like trying to SH + quick aerial against a character Diddy or shorter you might as well tear your hair out lol. A few things feel out of place as well: Bair lingers for a good period of time but it also feels like there's a huge additional window after the move is "done" that if you land you will get the full landing lag. I'd even take the move being shortened if it meant he could land easier with it. Dair multi hits occur way too quickly, a Mario-esque approach would be better (but still keep the properties of the move near the end that pop people up, that's still really good).
I would overhaul how Down B interacts, I think the move is basically worthless besides edge guarding. The tripping mechanic works out poorly for Squirtle if the opponent knows his full blown teching options (the teching window feels large), and it's already currently aimed at being a special gimping move. Look at the grounded version, after someone eats it and techs away. Near worthless. I'd have Squirtle's initial Side B use (maybe ground only) kinda burst/dash him forward a good distance before reverting to the original speed we currently have. Squirtle is poor at getting inside because he tends to travel at the same speed regardless, so the only checks you mentally have to make are for mixups like wave dashing. If he approaches with Side B or from the air, there's not a huge difference in travel time and half of the time you will swat him out of his option even if you technically guessed a bit wrong.
Given a poor grab range, awkward aerials for shield pressure + not many strong grounded shield pressure moves, it skews the RPS game outside of Squirtle's favor. He not only is lackluster at really getting around shields or whittling them down, but he also doesn't have a great way to get inside or pin someone down. Having solid mobility or hitboxes are huge hurdles for him to deal with.
His throw game is lackluster overall: you can name multiple characters who can effortlessly CG Spacies, but Squirtle's Uthrow CG/Regrab game is pathetic. The move has too much end lag/not enough time for Squirtle to use the throw and then get a meaningful followup a lot of times. Compounded into this, his mobility/sliding (noticeably out of Wavedash if you grab out of it) limits his options if he is forced to throw on the fly. If Squirtle is moving forward and does Uthrow, the opponent can take advantage of this with DI behind him to ruin his followups. Not many other characters have that kind of issue, and even Luigi gets a noticeable chunk of time to get a followup. There's no real reason people like Ike Marth Mario Fox Ness Sonic etc etc should have the super free Uthrow or Dthrow options for comboing, and someone like Squirtle kinda gets shafted lol. His Dthrow is literally the only redeeming throw, and strictly for killing! That should change, make his Uthrow better.
Kill power wise, you basically have Usmash and Dthrow. Killing with anything else usually means you got a Bubble Beam Gimp: it's extremely rare to kill with Fsmash Dsmash. This limits Squirtle, especially for being a lower range character.