Against puff it's not a bad idea to approach her, cuz she can't do much out of her shield (other than rest of course). So you can shield pressure her with neutral-A (bugspray) to d-tilts and f-airs. Don't shield pressure with the u-tilt too much cuz she can rest out of shield during it's postlag, (though it does work really well if you're expecting a b-air out of shield from puff). Also, I personally like going for the d-thow to judgement when she's at low %s. I think it's better to try and go for it instead of landing just one n-air. Even if you get an 8 it's another potential combo, and a 6 will do fine also. I think it's an efficient risk to take.
u-tilt works very well against approaching puffs cuz it has so much priority. Be careful for HER u-tilt cuz whenever puff u-tilts g&w it's pretty much an automatic rest.
As far as recovering, i usually save my second jump, and spam f-airs out to keep puff away until i get into up-b'ing range. if you KNOW you can intercept her in the air with the up-b without getting punished, do it. otherwise sweetspot the edge.
for edge-guarding puff, assuming you just hit her UP and AWAY from the edge, I like to first throw sausages (which sometimes make puff recover lower). If she does recover under the sausages, i usually try to land a d-air since it's rips through puff's b-air (or any other puff aerial for that matter) from above. If you catch her recovering from below with a rising pound, try and punish her with an n-air/f-air or at LEAST a d-air during it's postlag.
also about g&w's d-air...as far as i know, if you fastfall it, it can't be shield grabbed between d-airs two hits. if you don't fastfall it, i'm pretty sure most chars can shield grab you right after d-airs first hit if you're in grabbing range, which is usually the case, unless you're fighting zelda lol.
It's always nice that alot of players don't even know that the d-air even has a second hit (:
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i got a couple vids up from the Princeton Intercollegiate tournament last week, grand finals of doubles and losers quarters are up for me so far, i'll post more as they come if you guys wanna check em out:
Losers Quarters
Qerb (G&W) vs. Goof (Falco)
Qerb (G&W) vs. Goof (Ganon)
Doubles Grand Finals
Mr. F (Puff) & Qerb (G&W) vs. Niko (Marth) & Tian (Falcon)
Edit: Hopefully my set with Scar was recorded it was really close, waiting on ppl to upload them though