Don't approach Snake, let him approach you. If he approaches you, he will make more mistakes, making it easier for you to get some damage in. I'm pretty sure that he can pull a grenade after or in the middle of our dair, making it hard to follow up, unless you space the follow up move well enough as to where you won't get hit by the grenade (which is possible, but kind of hard to get used to). Getting him into the air is the best thing you can do in this matchup. His only options in the air are nair (punish), bair (punish), or uair (punish). It's pretty easy to tell which one he will use too. If he starts fast falling and you're below him by just a little bit, and he's not far above the stage, he's gonna uair. If he is way above the stage, like at the top of the screen, He will fast fall nair. If you're way below him, but he isn't that far up above the stage, he will fast fall bair. He can do the Wave bounce grenade thing too, but if they do that alot, you can punish them for that as well. On the ground, just keep them away as long as possible until they put themselves into a punishable situation, and then get them back into the air. I've pulled off a few Dair -> Uair -> Utilt combo's and just led into some follow ups against a pretty good snake (Infern Angelis, in a money match), and if you can pull it off, then it works really well. The utilt puts them into the air so you can keep them in fear. Peach can really make snake worry with her pressure and defensive game, so abuse it. Fair spacing can really mess up snake, because of the follow up options you have afterwards. Fair -> Grab, Fair -> Jab, or Fair -> just run back and turnip pull are really the best options. Snake will probably try to dash attack, dacus, or just walk up and ftilt. If they dash attack or dacus, punish accordingly. If they ftilt, try to get away, or punish with a OoS Nair, or a grab/jab. Watch out for a grab out of the first ftilt, it can really mess you up.
That's all I got. Sorry if it doesn't help or anything... D: