From the vid there were a few things I noticed:
Don't play with grenades unless you can use them better than a snake player can (not likely) they just end up hurting you more than anything. Play with his spacing, keep close enough where he can't get nades out effectively, but far enough that he can't hit you with his tilts. Snake also can kill you at ~90 percent with his utilt, so be careful, no damage to G&W is good damage (unless you get a lot more than they get on you or you kill them, but I think you understand) He may have bucket braking, but he still gets KO'd pretty readily.
Learn your techchase, learn who the Dsmash is guaranteed on, who it never hits, I saw you try to Dsmash every time you grabbed Snake.
Using duck on falco and fox really messes with them, they are often not accustomed to approaching on characters like G&W.
You shouldn't use Dsmash oos, I know it seems good, seeing as it hits on both sides, but quite frankly, it ends up badly more often than not, best thing you can do is just UpB and reset the situation or do a SH aerial.
NEVER roll behind people, G&W has horrible rolls, either roll away (still not recommended) or UpB, which is the best option to every scary situation.
Also, gimping is pretty good, I saw one spot where you literally just had to grab the ledge, not even timed, and you would have killed Ivysaur at ~80%
Don't taunt, just crouch up and down quickly if you must.