Spam shield against G&W. Dthrow nair is scary but it doesn't matter that much if it's not going to kill you. G&W isn't going to run up an grab you unexpectedly like Fox, Falcon, Marth, Sheik, or Pikachu, and he's not going to SH laser pressure you like Falco. He runs/dashes exactly as fast as Mario/Doc so you can use that for intuitive comparison of where it's safe to shield. When you shield, G&W has no approach options. Spaced fair isn't bad, but dashes and wavedashes into reactive shields can mess up his spacings a lot. His fair is maximally -3 on shield but that's only if he hella delays hit. It will likely be shield-grabbable every time. Once he doesn't want to approach, pull turnips. Threaten that you can pull turnips, but then don't. See how he reacts to you pulling turnips and how he reacts to the spacing at which you pull turnips. He is faster than you so it is hard to catch him or corner him. You can't just run at him. Take it slow and make incremental neutral advantages. This is not to say play slow and campy, but don't try to over extend yourself. At the end of the day, low tiers' tools suck and they can't compete with "lame" play. Respect his fair, dtilt, and dair.
If we knew what exactly was giving you trouble, it would be easier to give advice.
