The Snake versus Dedede matchup is 60:40 Dedede's favor. I'm really tired right now so I'll just c/p what I wrote for the Dedede matchup summary thread.
The matchup between Dedede and Snake is a very interesting one. Snake is faster than Dedede; can camp better through grenades and the Nikita (but mostly grenades); utilizes explosives to smack Dedede around all over the stage; spkies Dedede off the stage with fair, racks up lots of damage with nair and dair; edgeguards well with a combination of mortars, C4, mines, and, surprisingly, his bair; and kills Dedede at a lower percentage than other characters due to his extremely strong ftilt, utilt, uair, and fsmash. Yet at the same time, Dedede is considered by many to be Snake’s worst matchup.
Snake has more tricks up his sleeve, sure, and he’ll most likely outcamp you since his Waddle Dees can’t always hold their own against grenades. But once you grab him, you have a very significant advantage. Not only can Snake be chaingrabbed to the edge of the stage, but once you throw him off you can hit him with a dtilt and gimp him very easily. Gimping Snake is an interesting ordeal. With most characters the phrase “gimp” is synonymous with “WoP”. However, due to the nature of Snake’s cypher (better vertical recovery than your upB, which translates to horizontal recovery thanks to DI), it is better, in my opinion, to stake spike him. Snake is particularly vulnerable to stage spiking due to the fact that his upB goes straight up first and then slowly gains horizontal momentum. This means that many times, even if Snake has not been stage spiked but is still under the stage and not in range of the ledge, Snake will cypher under the stage until he lets go and falls to his death (or C4s himself, in which case he’ll be in a slightly better position to recover, but ultimately still vulnerable). The best way to stage spike Snake is The King’s bair, though his fair works well to. Inhaling Snake and spitting him out under the ledge is a fun alternative to Dededecide and works just as well as fair, but setting it up can be difficult due to Snake’s relative resistance to Inhale (his bair outranges it and he can feed you grenades instead).
Edgeguarding Snake in general is an important thing to learn since you’ll probably spend a decent portion of the match doing it. If he ciphers close enough to the stage, grab him out of it, don't attack or throw, and wait for him to release on his own. He’ll have to C4 himself, taking an extra 15% damage, and try to get back to the stage again, where you’ll be waiting with bairs, fairs, or an fsmash. I know I said stage spiking was probably a better option than WoP earlier, but on several stages that’s not an option, so if you think you can, Wall away.
Inversely, Dedede needs to be careful when recovering against Snake as well. Nair and bair go through mortars, so they aren’t a terribly big issue unless the Snake really starts spamming them, at which point you’ll have to stop using aerials and use the super armor from Super Dedede Jump. If you do use the upB, don’t be surprised if the Snake player starts smiling as this is very exploitable on the descent. Fair, dair, nair, bair, ftilt, fsmash, Nikita… these are all things he can do to you while you’re airborne. According to M2K, dair kills Dedede off the ledge at about 100%. Fair kills even lower than that. Be EXTREMELY careful when recovering against Snake.
But before all this edgeguarding business comes into play, you’ll have to face eachother on the stage first. As I mentioned earlier, Snake will probably be outcamping you with his grenades and try to force you to approach. Before that, however, toss a waddle dee at him to provide you some cover against low grenades and mines. The optimal angle of attack for approaching Snake is an interesting debate. Dashing straight on opens you up to grenades, ftilts, jabs, mortarslides, and lots of other stuff. On the other hand, approaching from the air opens you up to grenade bounces, aerials, mortars, and his insane utilt (you should see the horizontal range on it, it’s ridiculous). Ultimately you have to make the call here on what is best for you to do. If he seems to be wanting to continue to spam grenades, follow your Waddle Dees over there and RAR a bair when you’re close enough. If you start to approach and he begins a mortarslide, shieldgrab him and either chaingrab (provided the mortar isn’t heading towards you or didn’t go off for some reason) or fthrow/bthrow (the more likely choice). Of course, the BEST way to approach Snake is from below. Your utilt will probably not be what kills him in this match so feel free to set him up in the air and follow up with whatever you can throw at him. Uair, another utilt, you name it.
About Snakes explosives. Mines aren’t that big a deal since, as mentioned before, Waddle Dees can trip them easily. C4 is more dangerous and you’ll most likely be forced to avoid it. However, most Snakes will not leave their C4 in one place for too long (it explodes after 25 to 30 seconds anyway), and when you get them off the stage the first thing they do after cypher is detonate their C4 to try recovering back that way. Nikita is pretty easy to avoid if you’re not careless and not much else about it is worth mentioning. Snake’s most notable explosives are his grenades. A good Snake player can and will do tons of different things about them. Not just simple stuff like camping and bouncing, but advanced things like dropping a grenade in front of you, rolling behind you, cracking you neck a few times, and then throwing you into it as it explodes. Hell, I’m surprised nobody’s written a full guide about grenades yet. It’s also worth mentioning that many Snakes will mash B during the chaingrab since there is a very, very small window of opportunity (like 1 frame) for them to pull a grenade and stop your CG, but this is unlikely to happen and if you’re chaingrabbing properly it won’t matter much anyway.
Good Stages:
Final Destination, Pokemon Stadium 1, Rainbow Cruise
Big flat stages, weird ledges, no platforms, walls, and moving stages generally aren’t that good for Snake. Pokemon Stadium in particular is great in this matchup due to its odd ledges that Snake can’t cipher around and its walls on the rock and fire portions of the stage.
Bad Stages:
Battlefield, Lylat Cruise, Norfair
Stages with lots of platforms, congested stages, anywhere you can’t really get a good amount of spacing from Snake.
Another stage worth mentioning is Smashville. Though Snake players generally enjoy it for the moving platform since it’s a good place to put explosives, Dedede players also love it because of chaingrabbing tricks associates with it. Also, both Snake’s and Dedede’s utilts can reach through the platform to kill. This stage doesn’t particularly favor one character over the other, but I still felt it was worth mentioning since you may see it a lot against Snake.
I have a good deal of familiarity against Snake since my best friend from back home is a Snake main (pretty good too) and we played on a semi-daily basis over the summer, so I'll probably add more stuff another time.
