I've fought a few good ones online, and a few here and there that I've met on Smashboards, enough to know that Pikachu just has a lot going for him in the matchup.
- Multihit aerials will always tie, or hit Luma ( and generally Rosalina too, if she was intending to go in with a Luma aerial ), so Pikachu can challenge all of her quickest aerial options, leaving the Rosalina to rely on her slower zoning options. In addition, Pika benefits from the electrical on-hit delay, causing moves that hit Luma to remain active longer in order to clip Rosalina.
- Quick attack is a fairly safe zone breaker that leads to up tilts, juggles, and smashes. The only counter to which seems to be throwing out large hitboxes, and hoping you guess right on his angle of approach. As Rosalina, you generally want to keep foes from charging into melee range, but in this matchup, it's nearly impossible. It's also very difficult to edgeguard Pika once he gets within quick attack range of the stage, as he can simply wait for you to dedicate to an attack, then zoom around you to make it back.
- Thundershock ( The neutral b, whatever it's called ) is just the noncommittal projectile approach tool that Rosalina has issues with. Using gravitational pull, even while short hopping backwards, is slow enough that you're generally going to eat an up smash, or a combo punish of Pikachu's choosing.
- Not the largest issue, but Pika has several animations that cause him to sink very low to the ground, reducing the effectiveness of one of her greatest tools, her jab ( Landing lag of back air, end lag of dash attack, and several others leave Pikachu flat against the ground ).
The issue with this matchup is Pika has all the tools to stick to Rosalina. Her fastest options in the air lose to almost everything Pika has, her wait and punish gameplan is a gamble to pull off, and her offense relies on using her generally slow hitboxes that a skilled Pikachu would have no problem avoiding and punishing. The character outright prevents Rosalina from using the tools that make her unique, and that makes him incredibly frustrating to play against.
At the theoretically highest level of play, I suspect this matchup will be something along the lines of 35-65 in Pikachu's favor. It might not seem that bad right now because of shaky representation of the character, but his tools line up perfectly to counter Rosalina's.
Edit:
I'd have to agree with the Pikachu matchup. Fighting against a really good Pikachu player who utilizes the thundershocks, quick attack into smash attacks and thunderbolts is a really annoying fight.
I have a question though. How does Rosalina fair against Fox players? I fight against a really good Fox player who uses the Infinite Jab combos, running Up Smashes, up-tilts, ledge guards and basically everything that would make Fox a pain.
How can I safely keep him at a distance, and if that doesn't work how can I combat his tilts/running smashes?
Can't quite remember if we've covered the Fox matchup, but I'll answer what I can quickly:
- the Fox jab infinite is very shaky against Rosalina. Just hold up and mash jump, and you'll generally get out of it after one or two sets. Of course, he's still free to jab-jab-upsmash, but that's getting off easy compared to most other fighters.
- down tilt is a pretty good deterrent against running smashes, grabs, and dash attacks, so it's a solid option if you only expect him to make a grounded approach. His nair approaches are decently countered by up smash, or pivoting back into a tilt or smash. With that in mind, it all comes down to conditioning, and reading how he'll approach, and guessing right more often than not.
- I really don't see Fox as a grade A edgeguarder. He's got the standard ledge getup pressure that most have access to, and his offstage threat isn't particularly high with how fragile he is out there. On the other hand, Rosalina should decimate him offstage. If he ever has to use his up b to recover, he should lose the stock. There's no excuse not to go out there and hit him out of the very clear charging period. Edgeguarding his side b is a bit more difficult if he's sweetspotting the ledge ( if he goes over, any of your tilts should beat it cleanly ), so try to avoid aggressively trying to gimp that tool, but rather pressure him on getup with jabs.