Alrighty, time to actually contribute to this. Will be split up in multiple parts about key parts of the MU IMO.
1. On-stage control
Having control of the stage is important for all characters, but it applies especially for Rosalina and Zelda. Unfortunately for Zelda, Rosalina has the edge in this aspect due to the sheer fact that Luma is there. In general, Rosalina has a great ground game, whether it is from Ftilt, to Fsmash and Dsmash, while also getting good conversions on a grab. Luma makes Zelda's approach hard to a certain extent. However, as noted before, Luma is relatively easy to rid for Zelda compared to other characters, all because Rosalina is indeed using Luma extensively, and that Zelda has plenty of tools to bring it out of commission for a while, such as dash attack and to a lesser extent, Din's. When Luma is gone, the ground game is mostly even, so it's up to the individual player to see who can maintain stage control better. Dtilt and Nayru's Love will be seen most with Zelda in this situation, and to a lesser extent, her projectiles, so Rosalina has to be wary of her approach, if she needs to.
2. Air game
This is where Rosalina should capitalize the most. Comboing Zelda is relatively easy compared to others due to her limited air options. Nair and Fair cover so much of Zelda's ability to get in, while Dthrow Uair strings aren't rare either. Worse of all, Uair can kill extremely early, but this can be mitigated by removing Luma (as iirc, it's Luma's Uair hit that can kill early). Most of Zelda's air options are kill options, and as Rosalina is a big target, might be easier than a Rosalina player can expect. But this is where Rosalina HAS to do most of her damage, and should rightfully do so.
3. Platforms and Ledges
It's no surprise that both characters love platforms, but this again goes to Rosalina's favour. Uair, Nair and Fair greatly appreciate some extra platforms to help lock down the opponent and put them in a bad situation. Zelda can attempt to use the platforms to do Farore's Wind ledge cancel shenanigans or Uair stuff, but this generally helps Rosalina a LOT more. As for ledge options, should Rosalina be hanging on the ledge, Zelda doesn't have too many options to punish her get-up options. This cannot be said the same for the opposite situation, however, as Luma already covers one possible get-up option, and Rosalina in general does very well in punishing an opponent should he/she gets back on stage predictably with Nair, Fair, Dsmash and grabs.
4. Off Stage Game
This is where Zelda should be excelling, should she had met the requirements to get to this point of the game in the first place. People here seem to underestimate Zelda's edgeguard game, but for a character who may not be ranked very high at the moment, Zelda has GREAT edgeguard tools. Dtilt essentially guards the stage's ledges, as even a well-timed UpB from Rosalina may still get her hit by the move. Rosalina is a big target too, so Lightning Kicks, Dair and Uair are still very easy for Zelda to land. And don't be surprised if Zelda decides to commit offstage to hit you; Farore's Wind easily gets you back on stage after she attempts to kick you, putting Rosalina's subpar recovery on her toes. For Rosalina, edgeguarding Zelda is a bit too tricky, especially when she can actually retaliate big time WHILE she's recovering, so it's best to let her get back on the ledge/stage and punish her there.
5. Other Notes
- Both characters want to grab each other to gain momentum with grab combos. Keep your shield up and prepare to roll/spot-dodge when needed
- Whoever approaches is not favoured in the MU.
- USmash, Fair, Nair, Uair, Dash Attack and Luma are Rosalina's best options (I think) here
- Uair and Fsmash from Rosalina can kill relatively early
- Zelda's OoS UpB is pretty good in this MU, and can kill really early due to Rosalina's weight. Rosalina players have to be wary of this to maintain momentum.
- Since Zelda is mostly playing catchup in this MU, getting the early kills is key to take momentum. Well-timed kicks and Farore's is key.
- Rosalina stole our Dsmash and Fsmash.
ccccc
Stages
Rosalina - Duck Hunt, Halberd, Lylat Cruise
Zelda - Final Destination, Delfino Plaza
Neutral - Battlefield, Smashville
Key points to the MU
: Maintain stage control, play a solid air game, use Luma efficiently without getting it killed.
: Kill Luma ASAP, edgeguard efficiently, net early KOs.
Overall
6: 4
And you guys thought I was a troll smh. :^)