Don't stand still. Otherwise your shield will be ***** by Bair. GW Nair is useful as it covers a lot of space and makes it hard to get near him at times. Space correctly and abuse your Nair, it gives you a lot of options compared to Fair when your playing GW(it eats through most of his aerial;s and hits all at the same time). If your opponent spams Upb>Dair use your counter. Don't spotdodge when GW uses Fsmash as it lasts long enough to hit you even after you dodge. Tech when you hit the ground from GW down throw otherwise you could take Dtilt,Dsmash or Fsmash. Abuse Marths range with his tilts and SideB. Thats all I can think of.OH And don't spam any smashes as it will leave you open if you miss and I guarantee you, GW can punish a missed smash.