Ah, Snake dittos. Most people seem to hate them, but I enjoy them. This matchup isn't really as complex as most of the other top tier ones, but I'll write something up since Fatal and I end up doing Snake dittos almost every tourney.
Some things to note are Snake does a good job of edge guarding himself. Make sure you utilize this. He can also camp himself, though Snake can approach himself really well too. Getting Snake in the air or off stage is also a great way to give yourself a massive advantage, as Snake always ***** the ground.
Pivot grabbing Snake's landings are a great idea in this matchup. If Snake is coming towards you with him facing you, a pivot grab will snag him, unless he pivot nades instead. If you predict the pivot nades, just grab the Snake right before he lands.
Ftilting works great for both Snakes, it comes down to who is better at landing it and who is less predictable with it. You can punish a whiffed ftilt out of shield with your own ftilt quite easily.
Killing Snake in Snake dittos is very tricky sometimes. While you have many kill moves, when the opponent is at high % they'll expect the predictable utilt KO and hide in shield until you throw it out and just ftilt you. This means, read and bait. If your opponent has sidestep habits at those kind of up close situations, bait it and utilt him after it. If it's a roll, wait for it then kill. If he just hides in shield, grab him, dthrow, then attempt to tech chase KO.
Speaking of which, tech chasing in this matchup can be weird. Snake's roll away goes VERY far and pretty fast. It's almost unpublishable, and is unpublishable unless you predict it. You cannot react to it and re-grab. So instead, if you think it's coming, you can try for a grab or you can run and ftilt or simply Dacus. If you grab near the edge though, you can tech chase pretty well. Snake's getup attack is pathetic, his getup to jab is pretty hard to punish, but that's about it. Sometimes Bthrow is a better throw option, but when the Snake is at kill %, nothing is more reliable than dthrow to tech chase KO attempt. 9/10 times if they're smart, they'll try to roll away to avoid the utilt punish ;D.
And speaking of Dacus, don't mindlessly approach with it. It's very punishable on shield. You can be pivot grabbed out of it, ftilted out of it, shielded then punished, or even fsmashed with good spacing. Use it to get to the edge faster to edge guard. What I've been doing lately with dacus is using it to punish if I can't reach with an ftilt or utilt. Instead of a regular dash attack, I do the dacus that's activated when you hit the opponent. This one is much better for punishing than a regular Dacus IMO. With regular Dacus, the hitboxes change and you may miss punishing them. With 100% hitting with dash attack first, you're guaranteed the punish and even may pop them up in the air and hit them with the usmash.
Moving onto explosives, all of them are useful in this matchup. Even the Nikita. I try to keep nades out or around me at all times, it screws up the other Snake quite a bit. But you need to be good at dealing with the opponents nades and dodging them as there can be up to 4 nades at once on the field. Mines can be pretty useful, as if your opponent likes to Dacus they may Dacus right into it eventually. However, you may too if you forget about it. When I'm at high %, I usually don't charge the mine. If I'm at low %, fully charge is a good idea. As for C4, I find using it to KO works really well if you're good at hiding it. It also depends how good your opponent is at keeping track of it, or even yourself. And Nikita? Ally/Fatal love to use it on Snakes that recover high. It makes the Snake nervous and if it catches them, it could be an instant early KO.
Edge guarding is very important in this matchup. Just like with other characters, they thrive on edge guarding Snake for those early quick kills. You have many options to edgeguard with. Usmash, Nades, C4/Mines, even Fairs off stage (I wouldn't recommend this too often, even in a Snake ditto). What I like to do a lot is to cover Snake's landing options around a certain area. I'll drop a nade right next to the ledge and walk away from it and charge a usmash so that no matter what, the Snake will most likely get hit by something. Putting a mine near the edge can help greatly too, though Snake can pull out a nade and perfect shield land on it. Do note that. Also cooking a nade and tossing it up at Snake's Up B can net you an early KO if the Snake doesn't expect it.
As for recovering yourself, I'd mostly go for recovering high and fast. Landing can be tricky against smart Snakes, because pivot grab covers a lot of your options, and being predictable with pivot nade isn't a great idea, so mix it up a lot. Rarely do you wanna land with a Bair/Nair/Uair, but sometimes it can work well as a surprise, especially if you wait until nearly the very last possible frame to land a Bair on the ground.
Overall, just like any ditto, it comes down to who's the better and smarter player. Don't get ***** by explosives or ftilt spammed. This is a very bad matchup to have sidestep/rolling habits in, you do not want to eat ftilts the entire match.
