First off, in this matchup, it's a supergood idea to dodge manually.
That is, if he's approaching, walk or run away. Or jump.
Now a short list of things you can take advantage of:
D-air:
- Most GAW's will follow this up with smashes. However, it's possible to do a running/sliding shield into this ('neutralizes' its push, so you can grab him out of it). Just keep in mind that it has a fall attackbox and a landing attack box, so don't grab TOO early. If you can P-shield, do it.
- Another interesting thing to note is that when you U-throw, GAW will try to outprioritize you. This is successful for the most part. However, here's an interesting situation: U-throw>Spring>U-air kill.
Now, GAW is about 20% lighter than Marth (eg, 115% for that kill to work on marth = 95% for GAW). If you do this at 95% on an unstale U-throw, it will count as a combo. However, chances are you won't have an unstale U-throw, and hitstun will be lowered, so he can D-air you and possibly either Keyspike you down or hit you with the late hit and send you flying upwards for the death. You can take advantage of this and throw him at 115-120%. Why? Because he will do a D-air stall, but in the perfect height range for YOUR u-air to outprioritize him.
Keep in mind % adjustments for DI and when you're chasing.
F-air:
- I believe this is the most punishable of his aerials. It has the highest landing lag of all his aerials, so a whiffed one means a free attack. Since it's a 'single hit' attack, you can shield it once and render it useless.
Some counters to this move would be:
- - walking out of range and punishing with your move of choice.
- - "Reverse stutter step" (Perform a back>forward+A at dashdance speed) - which is nice if they're not doing WOP and try to "tip" you with it.
B-air:
- I haven't personally used this yet, but I saw on a thread in the GAW forums that if you have high enough shield, by all means, shield this move (and I'm not sure, but I think it said to dodge the final hit) and then grab him. Remember that since you have such amazing mobility, you can play hit and run until your shield returns. Reverse stutterstep works against this as well.
I believe that for both B-air and F-air, if you get the timing correctly, you can do a spincharge and hit UNDER him while he's in the air.
Smashes:
- GAW's F and Dsmash have lesser priority after their initial hit, and their power goes down, like a sexkick. If he misses, you can choose to clang your attacks with these (clanging generally isn't a good idea against GAW since your post-clang moves can be stopped by his much-faster tilts/jabs).
...or smash him out of it.
Also keep in mind that his Fsmash, Dsmash, and dash attack have deceptive hitboxes.
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Now for the random stuff that may be wrong:
Clangs:
- Sonic's Dash attack/spincharge vs: GAW D-tilt/jab
Keep in mind that as of this post, I've been playing Falcon a bit too much, so I'm not sure if this was done with Sonic's Fsmash or Falcon Punch >_>
- Punch defeats/outranges GAW's... Jab, D-tilt, F-tilt (?)