After playing my GaW against both Forward and DSF at AZOneTwoStep, I'm going to join up with the "Learn a new character" side here. Snake's tilts will destroy you completely. His knee has more range than anything you have except your Dtilt and possibly Dsmash, not that you'll ever get a chance to use the smash. The Snakes I mentioned stay on you with tilts and neither think about camping ever. Heck, Forward will NEVER use C4 unless he's sticking it to you or recovering with it. Not ever, I saw him put it on the ground once the whole tournament, but only when he missed a stick. They have the tilt spacing and timing perfected, if I tried to run away a few feet to bring out my turtle they would either mortar slide through me or just drop a nade and roll away.
I played probably 4 or 5 games against Forward and 2 games against DSF, I was trying to find a way to approach them the entire time. The only move that worked for me was Dtilt, it wasn't nearly enough.
I'll be the first to say that I'm not a good Game and Watch, mediocre at best. But I don't see any way to approach the close-quarters Snake. I say close-quarters because I have played a decent amount of friendlies against the Snake that took 5th at AZOTS, who is a more explosive-minded Snake. I can't beat him, because he's just plain better than me, but at least I can hurt him.
Key through mortar is neat, but they just roll away, dodge, or shield. Don't expect to hit them with it. Personally, I plan to pick up Falco or ROB if I ever expect to win against a great Snake.
Of course, if anybody has found a method of approach that works against an excellent Snake player, I'm all ears.