Projectiles....G&W hates them. Since they're not energy based, he can't use the bucket to absorb them. Don't spam them, but use them as you jumping away to keep him off balance, and than rush in for dash, up smash, bair/ fair combos. G&W is good and quite annoying for Toon Link, but Toon Link does have the edge.
Watch out for the turtle and the key. The turtle has hit stun has does a lot of damage. The key is quick has two hits
1) the downward strike
2) when it hits the ground, it has a "shockwave" effect that hurts you if you're too close to it.
Its also hard to tell when his sidestep starts and ends. I recommend using d smash or up B. Also, make sure you get your fast falls and shielding down. Especailly the sheild. DO NOT LET GO. G&W has lot of areral priority, and he can keep you in the air with his u air. His attacks have long frames (f smash for instance) and you will think they are over before they really are.
That's pretty much it. You should do very well with those techniques.