1. When Snake is falling back to the stage without the need of a cypher, it's usually better to just wait and grab again than to risk damage with a shuttle loop. I recommend, but not limit you to, aerial SLing if you can A) mix up w/ it safely (make sure you don't get predictable w/ it so Snake doesn't expect it) or B) when you predict he's going to cypher. Even if Snake manages to get back on-stage after he gets throwed like I recommend, Snake is so godawful descending into the ground that you should just juggle him with Uairs should he descend while he's on-stage (or if he likes to air-dodge, just wait and grab once more).
2. Don't approach Snake with tornados that low (especially when you were descending straight into the ground following with a tornado at point blank) or from very far. If you're going to approach him with it, do so higher in the air so he can't just blow it up while holding nades in his regular "holding-nade" stance, and if he shields and there are platforms nearby, retreat to those. You generally want to use tornado if Snake likes to be spammy with his ftilts, to punish his aerials, to do some potentially gay stuff like Uair 5x into tornado (provided of course you're high enough) and to just shield poke him if his shield isn't full.
3. I liked your first kill with the SL platform cancels; it was very effective based on Snake's positioning. I've actually never done that before but I'm probably going to practice it now lol
4. Picking up a nade when Snake's that close (at the beginning of his second stock) is kinda risky. If you wanna do something dumb to Snake while he's close to his own nades I suggest either not picking it up and do something else or catch him off-guard with a ground SL to hit Snake with the blown up nade while you don't get hurt (and if there are two nades, depending on the distance and positioning between you, the nades, and Snake, the explosion range can hit Snake from a ridiculous distance LOL).
5. When you send Snake in the air, while Uairing to juggle is ideal, you usually don't want to just go straight up and chase him, cuz he can just air dodge through you and now suddenly the positions have reversed. What you want to do depends on how far from up Snake is descending and his positioning. Here are a list of viable options for keeping Snake in the air:
A) if he's just doing a regular-fall air-dodge (like if he's doing so while descending back on-stage), grab if he lands, Uair if he's still in the air. Should the latter occur, keep Uairing him as long as you can until he manages to get out of it (ideally you want to just keep chipping in damage with the Uairs) or use other aerials if he's still in the air but positioned so that the Uair can't hit him but something like your side aerials can.
B) if he's really high up: maintain a distance between you and Snake while baiting him with Uairs. The idea is to get him to do something like air dodging, nade-landing, aerials, etc. but because of the distance between the two of you, you'll be able to catch him on time to punish him for it.
6. Be careful with full-hop side-aerials like your Fair right before Snake killed you for it and your Bair when your second stock started. You don't really want to do that in general unless you're playing someone like Wario who jumps in the air a lot and in that case you can use it as a mixup but it's generally not a good option.
7. When Snake is real high in the air, you don't really wanna tornado unless you catch him doing something that'll get him punished for it, but even then there are better options nowadays. See #5.
8. Careful with dash-attacking Snake while he's still grounded. Save it for reads and punishes.
9. Be careful with gliding to Snake and using your glide-attack while he's shielding. It's really tricky to utilize the GA properly without getting punished for it so it's reasonably risky but don't just GA into his face like that lol.
10. Dsmashing Snake that close when you're at that % is usually not a good idea, especially when it's your last stock. I would've preferred you just shield and grab right when he spot-dodged. Sometimes just standing and shield-camping will frighten the Snake into a spot-dodge, so if he tends to do that then take advantage of it.
You generally want to approach this MU by just camping him out and punishing accordingly. Virtually all of Snake's attacks be punished with grabs, so grabs are SUPER IMPORTANT in this MU. Take advantage of MK's ability to punish in the air and landings since that is one of Snake's greatest weaknesses, especially in this MU. Snake should not get back to the ground most of the time without taking damage, or worse, getting hit back off-stage/in the air again and thus putting him into a perpetually terrible position until he can somehow finally go through MK's punishes. Experiment with utilizing different ways to use Snake's nades against him back; you can get pretty creative and have fun with them that way, as long as you're hitting Snake with them of course
And let me stress that obviously most of these strategies are not always 100% viable so don't fret if Snake occasionally manages to avoid any of them (so long as he isn't avoiding them most of the time lol). Mix up to throw Snakes off and not read you easily, but don't mix up so much that the MU will essentially turn even all of a sudden because you're not taking advantage of MK's strengths against the character. That was my mistake for a while but I've only VERY recently learned to maintain a balance between the two (mix-ups and abusing MK's strengths). Finally, I would like to expand upon Isai's advice: Don't get hit,
and just hit things. Don't even worry about kill moves unless you KNOW for certain they're going to hit. Just focus on getting damage on your opponent safely and avoid getting hit so that it'll get to the point where he's at such a high % that moves that don't normally kill him will now do so, and if you played patient enough, you won't have taken much damage at least, so they'll be so scared to approach you that it'll psychologically **** with their heads and hopefully make them choke into opening themselves up for the final blow. Also get more grabby when they're at kill %, as most people tend to shield more often at that point.
Btw guys this is my first time critiquing anything ever so I'm sorry if I may have missed some other useful stuff but I wanna help people get better and I've always wanted to do critiques lol