I'm super late on this response lol, but I'm gonna respond to Jtsm matches.
vs Falco
You never went for stickies this MU which confuses me since this is like the STRONGEST part of Snake's gameplay and one of the MU where it's relatively free in terms of setups into it with CG's...
Ducking is pretty good in this MU and you should try to powershield lasers from it, and seriously, you REALLY need to start using Snake's DACUS, it's literally his best approach options, it's his only move which allows him to commit forward that fast, and it's REALLY good to do from ducking, if you used it in this match it would have helped loads.
I think I saw you use it like once, I don't think you realize how useful Snake's DACUS is, because if you did you would definitely be using it more often.
Also, your edgeguarding is a major issue, 1:51, 7:29 your first instinct is to plant a mine, and jump back and shoot a Nikita, but let's actually think about this practically and what you actually get from it...you give falco a free edge because the Nikita won't get to him in time, and the most he can do it get hit by the mine at like 70%, survive, and then back to neutral.
Commit to something, shoot a missile at him straight away, jump out and Fair him or Bair him, F-Smash if you think they will Forward B, but don't plant a mine, jump back and shoot a Nikita on such a fast recovery (or MOST recoveries), it feels a lot more effective then it actually mostly is.
You never instinctively try to edgeguard people, like @ 2:18 and 5:24 with Falco high percent you could walk Falco to the edge and throw him off and try to edgeguard him, but your first reaction is to U-Throw Falco, and what do you really get from it, he goes in there, hits the floor, the neutral game begins again. It lost you the first game along with not just jumping on the edge when he off the stage
And remember this MU is super free for C4 sticks and CG's, 4:08 you should have just went for a stick instead of a U-Tilt or even throwing Falco off the stage
vs Sheik
Even at 5:25, when Sheik was really far off the edge, look at what your first instinct was to do instead of just simply grabbing on the edge lol.
Look through this match and you'll be able to see the times you throw Sheik off the edge and then basically just let her grab the edge for free, all you need to do is grab the edge and then force her to come on stage and punish her with a stick or grab
Please don't CG, into Up B (1:19, 3:31, 6:28, 7:50) it REALLY doesn't work, all you get is an Up B and the opponent can DI left of right to escape a follow up, you could of got a C4 stick, Uair, or Fair which is much more effective.
2:11 is why I brought up saying your edgeguarding is a problem, literally all you needed to do was jump on the edge, and jump up and either Fair, or Bair sheik back off the edge or even UAir, but it never seems like you instinctively have that in mind and you need to get your gameplay to that point. You literally went from 38% to 121% for not capitalizing on that.
vs Sonic
I agree with most of what Sax said, overall I just think it's your fundamentals that need improving