Here from the Puff Boards to speak on the behalf of our bubblegum overlords.
JIGGLYPUFF ADVANTAGES:
Rosalina is tall, floaty, and light, which means she's subsceptible to our rest setups. Chances are that if we land a SHFF'd Uair at 35%ish or higher, she's toast. I could see her being vulnerable to juggles as well, although her Dair is pretty good so I doubt it works in practice.
I'd say that as far as aerials go they're pretty close- Rosalina has slightly better disjoint on hers, and the frame data seems about similar. Of course, its worse if we can land the hit, depending on the scenario and the aerial we used (Beware the Bair.) What Nair lack in range it makes up for in speed, so if we're close enough it can beat out Rosie's aerials before the hitboxes even come out.
Jigglypuff also has quite a few ways in which she can deal with Luma. A common tactic for Puff players to use is the Retreating Fair, because it's a quick poke that's safe on shield; Against Rosie, it's easily abusable to chip away at Luma. Retreating Dair is riskier, but if you can get all the hits in it does 14%. Pound in particular straight-up murders Luma. 11% AND it sends the poor little guy flying! It's also yet another move that's safe on shield if used correctly. If those don't work, Jigglypuff can easily just float over Luma's pointy head. Good luck Landing Luma Shot on us, at least on the ground.
Launch Star is pretty much edgeguard food for us, due to the lack of a hitbox and its semi-limited trajectory. If you go low, we can land a Bair and finish the job we started. Recovering high is a decent idea, because the momentum of the move after you've already started the helpless state propels you right past us. Of course, if we can predict that we'll just follow you for a free rest. Rosie's best bet is to just mix up her recovery as well as she can, because otherwise she's almost completely helpless to Jigglypuff. Star Bits are a nice spray to try and keep us away if we come in recklessly, but chances are no puff is going to extend that far offstage in this matchup. After all, you have to come back eventually... If Rosie has some other recovery tricks, please let me know so I can go over the .
ROSALINA ADVANTAGES:
Rosalina in my experience has a lot of tools for juggling, and Jigglypuff doesn't really have an answer when she's being juggled. Puffs should be wary when they're in the air, lest they stay there longer than they intended.
Although we have ways of clearing out Luma, when he's alive and kicking he's a verifiable powerhouse. His smash attacks are much scarier than Rosalina's, he can get at us from far away with Luma Shot, and Star Bits are frankly just annoying. Mark my words, Jiggs will be gunning for Luma. Keep this in mind and take advantage of the opportunities it presents.
Rosalina might be easy for us to break offstage, but when it's reversed she's no slouch herself. Dair is very, very bad for us, as are the majority of her aerials. Dair and Uair can outrange our Uair and Dair, respectively. Star Bits aren't super useful here but can eat one of our jumps and stop our momentum. The fact that we rely almost entirely on jumps makes it pivotal that we do NOT get hit by any of these. However, we still have the option to dodge, so.....yeah.
Onstage, Jigglypuff struggles with range and approaching. However, Rosalina herself doesn't have much outside of Luma's effective range, and Luma himself has zero disjoint whatsoever. Jigglypuff shouldn't have too much issue with getting in when the two are separated, and if they're together Jiggs can just abuse Retreating Fair.
Rosie of course beats Jigglypuff on the ground. This is something that Puff is used to, so don't expect to get much use out of it. However, it's worth noting that she may occasionally go in for a grab, as our grab game is....bizarrely decent this time around. Not too much of an issue, considering Luma's ability to absolutely wreck grabs.
Additional notes:
-Knowing Jigglypuff's basic attributes, dthrow to fair is unlikely to work very reliably. I could be wrong on this, but otherwise assume the worst. Since Jiggs is generally hard to grab anyways, don't expect it to be particularly useful.
-It's generally accepted in the Puff Boards that dash attack is the most underrated broken move ever. Look out for it, as it comes out pretty fast and can kill if it hits clean.
-Utilt is an alternative kill move at high percents, as is Uthrow in extreme conditions (requires high percent, rage, and platform placement)
-Our crouch is one of the lowest in the game. It shouldn't be an issue with Luma around, but it's dangerous to go alone. Take this!
Overall it's close, but I'd say that we just have an easier time getting kills on Rosalina. We can edgeguard her more easily, and our rest setups work like a charm in this matchup. We can also clear out Rosalina's greatest asset, Luma, with relative ease. However, if Rosie can play it right she can keep us from getting in to attack.
55:45 Puff doesn't seem too far off to me, maybe a little less or even a straight 50:50.