My take on the matchup since this is one that I actually have a lot of experience with and some level of success.
Most of the match will be spent by Ganon running away and leaving large painful hitboxes behind him in the form of bair and uair. Fair will rarely work in my experience, although it can trade sometime (moreso if puff isn't abusing bair for some reason). If Ganon can keep up his brick wall of bairs/uairs he can control the pace of the match pretty well. It's important to watch what Jiggs between your jump and DJ because sometimes she'll try to to pop you with a uair --> rest. If you call this, you can sometimes get her with a cross up stomp and then tech-chase. If she's still advancing and a stomp will be too slow or something, you should know when to waveland since that can provide a lot of space and perhaps give you the opportunity to hit her with an ftilt. The ability to platform dash out of a double-jump is also great since it gives you a way to either retreat momre quickly from jigg's great air speed or even move over/around her if cornered.
Going along with Ganon trying to brickwall jiggs, is the idea that Ganon needs to attack Jiggs at weird angles since going head-to-head against her feet often results in you just getting hit. Uair is great for this since it can hit at nearly any angle, and bair works well too since its got a lot of range. Another way to force jiggs to play a non-linear game is to utilize platforms (I do love my platform camping) and either force her to approach you from below (where her uair gets stuffed by stomp or she has to air-dodge to get around you) or she can try to get to your level indirectly (ie, go to the side of the stage and then start trying to approach horizontally again). If she does that, just drop down and now you're below her which is also a great position to be in. So platform camping probably isn't something you want to base your anti-puff strat around, but it can force puff into awkward situations and if nothing else, eat at a player's momentum. Also, being able to drop through platforms oos is a nice skill to have hear (and in general) since if she's ever pressuring you, you can just drop down and do a uair.
Grabs: Ganon's got a decent grab game against puff. Grabbing puff can be difficult if her spacing is spot on, but it's possible. Sadly, I'm not aware of any guarenteed ways to land a grab (except for stuff like shielded fsmash or something), but they do happen. I'm pretty sure low percents still should yield a guarenteed uair (bair if they di behind for some reason?) As said earlier, higher percents lead to usmash and fair (I've gotten it to work as low as high 50s/low 60s for fair). D-throw upair also kos at a semi-reasonable percent at most stages (90-low 100s. She should be dead far before this, but it's another option).
How to punish rest: Utilt has better base-knockback than Warlock Punch and fewer people know how to tech it. If utilt won't kill anyway I go for a double-stomp tech-chase grab --> attack, which if it doesn't kill her, will put her in ko percents. Avoiding rests is mostly a matter of watching the jiggs player's patterns (when does she stop jumping around and start doing uptilts/upairs?) and reacting from there. I think pound --> rest might work at some percents too, but that can be stopped by shielding --> punish or even an fsmash (thanks to the lean-back during the start-up). Another thing to consider is that when you ARE rested is how you should DI. If you're at low percents (very near 0%) survival DI (DI up I think? I only remember how to di during a match, haha) is probably you're best choice, since Ganon can recovery pretty well unmolested. If you're at higher percents, you might want to di towards the side blastzones since that way you can avoid the star-ko animation and still have a chance to beat the snot out of jiggs upon respawn.
Stages: Ganon naturally likes stages with close blast-lines where his raw strength can lead to early kos, however at the same time I think that Ganon needs space to run around and create weird attack situations for puff more than anything, so YS isn't my first choice for Ganon's cps vs puff. I'd actually pick PS first, since you can still get some star kos, and ganon has enough space to run around/away. BF is good too (as is YS, of course). I haven't tried FoD vs Jiggs, but I imagine due to the platform layout and high ceiling this would be a stage to avoid when possible. Corneria and Green Greens are also possible choices, but then you always run the risk of them pulling out fox. Ganon does well enough on neutrals anyway, imo.
As far as bans, most jiggs like MC, and some like Brinstar (seems like it would be okay for ganon, but I have never played there vs puff). If you want to ban a stage, MC is probably a safe bet, although it is still a winnable match there.
Again, just my experience with the matchup. Hope this is helpful/accurate.
