Okay..I'll give as much feedback as I can. I'm going to edit this post as I watch the rest of the videos too.
First of all: One of the most important things about playing Snake: Keep rolling at a minimum. You should be walking and dashing the most. You're rolling way too much, especially behind your opponent which is very dangerous. Snakedashing/mortar sliding doesn't be used as much to get around either. It can be shield-grabbed, as well as spotdodged and punished. You used it a lot to get up in Marth's face, which isn't the best way to handle that match-up. The Marth you played against also has a lot more work to do on his Marth, but I'm going to link you to the Marth match-up discussion so you have an easier time:
http://www.smashboards.com/showthread.php?p=5991695#post5991695
The other person who posted here was also correct: Snake's f-air is pretty useless. Sometimes you may have the opportunity to spike, but using it on while the opponent's on stage is too risky and easily punishable. Aerials you should be using are the n-air, which is great for stopping edge-guarding, stopping approaches, and can be used to mix-up your approach sometimes. It's also a decent kill move. You may also want to try using bair or dair OoS (out-of-shield) to surprise your opponent. Both are very strong aerials. Uair is also good for combo'ing and hitting an unsuspecting opponent while falling from your cypher.
Furthermore, spare your up tilt until your opponent is at high percentages. Lol, I saw you using it multiple times when your opponent had low damage. Utilt is pretty much your best kill move and the more you use it early on, the weaker it will get and the harder it will be to kill with it when the opponent has high damage. =/
Your projectile game needs a lot of work, especially your grenade game. You hardly use your grenades, and when you do, you don't cook them. There are plenty of ways to cook grenades, which you will find if you browse through these boards. Grenade countering is a very important technique you need to learn when playing Snake. You need to learn how to set-up the stage. I noticed you only played final destination, which in some cases is a good Snake stage, but you should also play others so you gain a better understanding of how and where to use Snakes explosives and projectiles. Use proximity mines when your opponent is off-stage and between stocks so you can limit your opponent's movement and force him into your own pace. The mortar is a good projectile to block off approaches and to edge-guard. Using it to approach may be helpful if your opponent likes to roll a lot, but against Marth it isn't so great as an approach. Marth has superior spacing and can easily keep you away from him without having to roll behind you. Also, don't explode your c4 every time your opponent comes close. It becomes predictable and it will lose its purpose of the opponent can predict it.
Another thing you want to work on is your recovery. Read a little more on survival DI and how to DI out of multi-hit attacks and combo setups. Reading your opponent's DI is also an important part of advancing your Snake game. For example, your friend won't always get hit by the dash attack and mortar when you mortar slide him. When you start expecting that, you can use it to your advantage and plan your strategy further. Anyway, I'm going to watch the last few matches. I know this might be a lot to read, but hopefully you'll learn some things. Don't worry, others will critique and elaborate further on what I have siad.
Good luck, fellow snake main. :>
Edit: Doh, I forgot one of the most important things about Snake: His grab game. You hardly grabbed and used the d-throw in your matches. Snake's d-throw is godly and his tech chasing is amazing. It's a great way to build damage and intimidate your opponent. Look up SuSa's guide to tech-chasing with d-throw and what you can do out of grabs. Grabs are one of Snake's best approaches and can be used with grenades, and can be used combo. You can throw your opponents into mines or throw them to where your c4 is and explode it and follow-up from there. Anyway, I hope this little bit helped too.
