I actually think it's kinda fun playing him. All you have to do is get him off stage.
Good advice.
I have yet to encounter the infinite and I was told that it only works for certain characters. My main gripe is not defeating her but just how frustrating the match is, even if you win. At least with the Ice Climbers (not the same thing but kinda the same in that they have unique mechanics that can be abused) is at least when you kill the buddy, it is satisfying in that you reduce its power tremendously. When you kill Luma, you still have Rosie and her ridic aerial moves. And then in no time Luma is back and you start all over.
I play as BJ and he is not the greatest character already but the match against Rosie is completely one sided unless you are super cautious.
The infinite technically "works" an almost any character, but in terms of carrying you off to the side, it's limited. It's still a great damage builder on pretty much anyone though. I believe Greninja might be immune to it though, from my testing, and characters like Bowser need to have a bit of damage on them already for it to work.
It's also great against Falco. Yesterday, I KO'd the same Falco twice because I carried him fairly far off stage with the infinite and then he dropped out of it, but because he was likely mashing buttons to get out of it (trying to attack Luma), he was committed to falling attack animations and fell too low to recover from them.
And yeah, BJ is one of Rosalina's extremely favourable match ups. She can use her Down B to negate his slow and predicable Neutral B (probably works on Up B too but I haven't tried), she can also use it to take control of his Mechakoopas and fling them back at him, Luma Shot goes right through BJ's Side B...
Utterly amazing advice. Normally I'm not this sarcastic but this just feels like it's not a real answer.
1. "Give up on your main, play as a character with the matchup advantage" isn't helpful both in the sense that it doesn't let a person grow with the character of their choice and to make matters worse we're specifically talking about For Glory here, a mode where you don't even know what character your opponent will use until the fight starts. So me picking a different character to tackle Rosalina when I may not be fighting Rosalina in the first place is silly.
2. This is more of an opinion thing than me finding actual flaws in your advice but I swear close-combat characters are the worst against her, especially on For Glory. Approaching her is extremely difficult and it's not like she's actually immune to projectiles. She just has that down special, which again, can be dealt with.
3. Unless we're talking about the infinite that only works on Sheik and Captain Falcon, this is not reassuring to anyone and only reinforces these outcries you've supposedly been hearing that Rosalina is overpowered. Also saying to watch out for the setups without explaining what the setups are is worthless advice. People who do not play as or against Rosalina a lot likely do not know how these infinites are performed.
1) I didn't say "give up on your main", I just gave characters with particularly good counter abilities. It's more for people who use multiple characters, and happen to have ZSS and Lucario as one of them, so they can use the main of theirs with a favourable match up. It's always good to use a wide array of characters to cover all kinds of match-ups. It's better advice than say, telling a Bowser Jr main to just get better with Bowser Jr, since Bowser Jr is INHERENTLY terrible against Rosalina. I'm giving people an alternative character as an example. ZSS is just an easy one off the top of my head.
2) Luma can block projectiles too, so that's another reason why projectile users are terrible against her. She can use Luma as a meat shield, approach, and since she's far better at close range than the projectile characters, she has them right where she wants them.
Luma is great against short/mid-range projectiles, and Gravitational Pull is great against long range ones. A fully charged Luma Shot also has extreme priority, and will go right through pretty much any projectile (and in most cases, will negate it entirely too). GP at close range is also great against large projectiles, as it makes Rosalina their "owner" as they spin around her, and because the projectile is so big, it will usually hit the opponent.
3) I'm talking about the same infinite, but the person who claimed it only works on CF and Sheik was not being specific enough. The infinite works on almost anyone, but CF and Sheik are the only ones you can carry off the side blast zone with it (so far).
The obvious set up is the grab release one - she grabs you from the air, has Luma ready a little bit away from her, intentionally releases you, at which point your grab release animation carries you right in front of Luma.
She could also fire Luma through an oncoming projectile and punish the projectile user with the infinite. Outside of For Glory, the Luma Warp custom special is perfect for setting up stuff like the infinite too, since it has virtually no ending lag. Luma's jab also makes him inch forward, so she could just inch him forward a bit to start the infinite if someone just happens to be really close.
I was making that post casually during some idle time in college. So expecting a comprehensive Rosalina counter guide is silly, they were just quick hints, especially since this thread is not even exclusively about Rosalina. If you want more details on how to counter Rosalina, you don't have to be a sarcastic, condescending douche about it, that gets you nowhere and does nothing for nobody. And frankly, makes NOT telling you anything seem preferable, so if I coincidentally ran into you in For Glory one day, my Rosalina would hand it to you. Karma! :D
Instead, you could check the Rosalina boards for more in-depth discussion on her, you could wait for a Rosalina & Luma counter guide to show up in the new Guides section of the site, or you could have even just PM me if you have more in-depth questions about the character.