Normally jigglypuff should be in the air. Against GW however this is suicide. GW's turtle beats out jigglypuff's aerials, including pound. Pound is as effective on GW as any other character, don't think it is a magic tool because of it's high priotiy.
Now I have mentioned that jigglypuff cannot fight GW in the air due to his superior priority and range, how are you exactly supposed to fight him? The answer is that you will be fighting this entire matchup with out of shield aerials and backwards shorthops (for spacing or for the spacing needed to land a Fair in)). Bair is almost completely useless in this matchup, GW's aerials give it a very tiny window where you can hit with it so when you find room to hit with it, use it. Most of this matchup should consist of your spaced Fairs, spaced grabs, and Nairs (preferably retreating and OoS). Rollout is useless in this matchup as it should be in every, don't use it.
Now from what I've mentioned, wracking damage up on GW is difficult. So with Fair stale, jiggs is left with four kill options, dash attack, rest, f smash and Dacus. Drill rest should be one of your main kill moves, it kills early and the risk is worth it because you're gonna die at like 80% anyways, why not go for it? Note that uptilt can be used as well. Dacus is used for its massive disjoint, punish his Dairs with it if you can. Dash attack is the surprise KO and f smash is meant to read his roles. I'll write more later when I have time.
GW is such a weird matchup for us because he forces us to play completely different. You have to hide in your shield from his aerials and do your best to counter them with OoS and AMAZING spacing. Idk about numbers exactly for this one, I've heard stuff ranged from 40:60 (burntsocks' opinion b/c of my jiggs) to 20:80. I'll do my best to play leepuff and see how that goes (lmao I'm gonna get *****) and mabey then I'll have a solid number.
Also green greens can be AMAZING for jiggs against gw. Just run the entire time and try to lure his retardedly big hitboxes into the exploding blocks. The low kill zones will mean you die early but so does he. This stage really is russian roulette because you don't know what the outcome will be.
Turtle doesn't really "beat out" her aerials, and it certainly doesn't beat out Pound. Here's the thing you need to know about turtle. It has ridiculously huge range and hits a bunch of times. It doesn't come out until frame 10. Actually, here's the first frame all of his aerials hit on:
nair: 7
fair: 10
bair: 10
uair: 6
dair: 12
Now, here's Jigglypuff:
nair: 6
fair: 8
bair: 8
uair: 8
dair: 5
Pound: 13
You have higher attack speed in the air and more mobility. Seriously, you can challenge Mr. Game & Watch in the air. His moves do NOT beat yours if you hit him first or even at the same time (particularly Pound!). The only reason they SEEM to beat yours out is because he's outspacing you and generally exploiting his range. Match his spacing with your timing. You are basically suggesting defining the game in terms of spacing. If you do that, you lose really badly. His spacing is better than yours; all he does is space. Of course you should still strive for good spacing, but you seriously do not want to allow the match to be defined in those terms. To put it more clearly, slow play seems rewarding to you at first since you don't lose as fast, but Mr. Game & Watch has inevitability on his side. If you slowly chip away at each other, he wins every time. You need to get in his face and press the attack. Seeing as you're Jigglypuff, that means taking to the air. Before you learn the matchup you'll lose a lot, but this is really the way to win.
Mr. Game & Watch has the best shield pressure game out of the entire cast. I'd rethink any strategies that involve heavy shield seeing as you don't have grenades or a frame 1 invincible up special or even a tether grab. Running from me in general is pretty useless; the more time you spend away from me the more time I have to set up optimal turtle spacing. It would be different if you had a projectile or something, but you don't. You don't even have a good move to stop my approaches like Shuttle Loop. In Jigglypuff's case, running is just delaying the inevitable.
All of your ground moves except a well timed Rollout are trivially stuffed by dtilt. DACUS is never going to hit me, for instance. Dash attack is decent as a surprise, but if you are ever predictable with it I am going to sit back and let my dtilt do the talking. Given that Jigglypuff has the single worst ground speed out of the entire cast, you don't really get many opportunities to be unpredictable unless you are in the air.
Rollout does punish me for charging smashes (it's actually probably the best punishment that any character has), and it's your only real hope of killing me under 100%. It does a lot of damage to the point where even if you only land half as many Rollouts as get punished (ones that just whiff and do nothing don't count, and if you do it right that's most likely anyway), you are winning. It's obviously a situational move, but I can say from the perspective of playing against Jigglypuff that it's one of the few things she has that makes me actually worry. I actually ban Final Destination when playing Thinkaman just so I don't have to deal with Rollout if I don't want to (I like playing on all of his reasonable CPs).
What doesn't worry me is Rest. Drillrest isn't a combo and isn't reasonable to land anyway since landing dair requires you to be right above me which is prime territory for my usmash, uspecial, nair, uair, and to a lesser extent utilt. Like, if you try this, I'm just going to uspecial you out of dair until you get the hint, and when you whiff Rest I'm going to punish you so hard with a fully charged smash that you'll wish you died as high as 80%. Really, just risk-reward wise, Rest is a terrible, terrible move. My fully charged usmash is pretty much the same thing except mine isn't really very punishable while yours lets me do literally anything for free. The only time I would seriously use Rest would be in situations where the stage is going to cancel the ending lag for you (water like on Delfino or something funky like springs on PictoChat). Otherwise it's a lot of risk with not nearly enough reward.
Your utilt isn't really practical since it doesn't really chain well against me (I'm light and floaty too!) and more importantly requires you and me to be right on top of each other on the ground which is pretty much never going to happen.
A note about my dair. I will really only use this into a platform or when we are both in the air. I'm not going to randomly dair into your shield or the ground within your DACUS range or anything unless you manage to legitimately fake me out which probably requires you to have been in the air in the first place. It's just not something you can rely on; good G&W are judicious with dair use since we know it gets punished otherwise.
That is... a great misrepresentation of Green Greens. Do you really think good G&W players are going to be lured into hitting exploding blocks? Russian roulette? You have to understand that good G&W play is all about being careful. The character is all spacing; I'm sure our huge hitboxes seem unwieldy to you, but we can maneuver that turtle like surgeons. If we hit those bombs, we won't be hurt. We will hit them deliberately when we are out of range. You also have no hope of outcamping us here. G&W is a ridiculously efficient camping character on Green Greens; only Snake can really match him. Basically, I'm going to sit on one of the side platforms when I'm up. You can either go through the blocks which makes it easy for me to turtle you or go over and around them which makes it easy for me to up special through you and then run to the other far platform. If you get the lead and try to do the same thing, the platforms are positioned almost literally perfectly for Chef. The low ceiling helps me more than you since my usmash is so good and you are forced to approach me from above so much. I have a ton of other little tricks on this stage too like how good the side platforms are for me, invincibility frames through blocks from below, dtilt locks on the blocks as walls, dsmash on the small platforms being just plain ridiculous, glide tossing apples... The thing furthest from the truth is that you never know what's going to happen on the stage. The stage is probably the single stage G&W is best at controlling.
I really think I know this matchup well, and I'm just trying to convey the things Jigglypuff can do that make it harder on me. It's uphill regardless, but that's really all the more reason you have to play actively and force your strengths.