What's stopping Kamek from amping himself and then overpowering her forcefield with his magic? His amp is powerful enough to make those affected massively stronger than base characters and virtually immune to their attacks.
Has Kamek actually ever done this? He can
transform into Giant Kamek (even
without his wand), though this doesn't seem to make him any less vulnerable, nor does his rage boosts in
Mario Party 10 and
Paper Jam Bros or the spell he uses to
heighten certain attributes of his clones, making me a bit confused on what this is referring to. I guess this is probably the spell he uses on bosses in Yoshi and NSMB games, though even then those just tend to be trickier bosses or enemies turning into boss battles, both still vulnerable. Even then, when it's
his own fight, he seems to use the spell for
an adding environmental twist. Due to its nature, it might be hard to aim it at himself, but I suppose he could think to have his clones do it for him if he really felt pushed to resort to such a strategy (though maybe he uses it on himself to become Giant Kamek? It does seem to have the same sort of visuals and audio. At which point, I don't think he's too immune to attacks in that state, and the Star Spin should serve as a means of
making him dizzy to exploit that weakness).
To not just write off the idea though, I assume this might be pulling from how his magic in the source of the Giant Bowser battle in NSMBW. This same spell is
used in NSMBU, where Giant Bowser
can still be harmed even
by power-ups, though since these battles serve different narrative purposes, you can probably just argue NSMBW Giant Bowser is built different, since if he could be beaten before the chase concludes, it wouldn't really work out (not to mention
he's immune to a
Synchro Ground Pound!). But since he's still vulnerable to a castle collapsing in on him, I suppose a theoretical Giant Kamek on that level (I feel like Bowser was a special case due to being the final boss even before the spell, putting him above the likes of Kamek and the other bosses to explain his untouchable nature compared to the norm, but we'll play along with the idea), Rosalina could resort to using the Mushroom Castle against him, since the battle location offers that nearby! The idea certainly spices up the battle, and would certainly provide an even bigger challenge to Rosalina, putting the ball in Kamek's court, but I wouldn't say it reaches the level of being unwinnable for her, as she can still exploit some of his weaknesses, or try to stop him ever reaching the point where he could pull it off.
This should put it around the level of Rosa's forcefield since it also takes no damage from Mario's jumps, so Kamek should be able to break through it with his Magic with enough attacks.
I don't quite think it would put him on the level of Rosalina's forcefields, since that was surviving a universe going through a big crunch and big bang on it. Even with the power boosts at his disposal, I don't think a High 6-A Kamek (as per OP) is reaching that sort of level. I guess I get where you're going by using Mario's attacks a metric, but don't think that's quite how durability scaling works. I'm not sure if Kamek would be so desperate to break the forcefields as to have to become Giant Kamek/amp himself just for that, especially when he has ways to work around it, but guess it would put him in a better position either way.
iirc Paper Jam, he just does it in the middle of the battle regardless of whether you used any bro attacks, so we will eventually just go for it.
I think it's a sort of retaliation spell, as if you
use the Jump attack instead of a Bros Attack,
he'll take away your Jump attack, so does seem as though it gives at least one free use of a certain technique. I guess you could argue that since both have prior knowledge (as per OP), Kamek might come in knowing what attacks/moves he'd want to aim for, but even in that battle, he seemingly won't aim for a Bros Attack (even with the knowledge of them being a thing) if you didn't use one against him in the turn before. This is certainly one of his more useful spells here, as it helps him whittle away at Rosalina's counters, but I do still feel like she adapts well/works well with a limited moveset to be able to work around it all the same.
He doesn't have to swap items when taking them, he only does it in Mario Party cause it's an in-universe game. If he wanted, he could just take the items and not give them back.
That's probably fair, yeah. It might be a kind of magic he can't really alter due to the nature of the spell, but odds are he can play around with it as you say. Though at that point, it seems to work the same as in Sticker Star and Super Mario Party (
which I finally got footage of, there reeee), at which point her same defences should apply. Concerning item theft, Rosalina has also had access to the
Fly Guy Ticket, the
Plunder Chest and
Boo as her own means to take things from Kamek, his wand would be especially useful (or tennis racket as you pointed out), though
he does seem to be able to summon another wand distinct from his usual, making it hard to permanently keep him away from the spells he requires a staff of some kind for. Comparatively, taking these items from Rosalina (not to mention their single use) will lock her out of such an ability without physically snatching things, which does give Kamek the advantage in this field.
He can still cast spells without his wand and can just take one off his duplicates if needed.
Not quite where I was going with this point, but I suppose so, yeah. I think generally it might be some spells don't require a wand (or at least a medium to channel the magic through), whilst others do, and even with the tennis racket it takes time to charge, which is when you'd want to strike to avoid the spell from being cast. Speed being equalised makes that somewhat hard, but the Luma paralysis does seem quite quickfire and should interrupt any nature of spell from being cast if they're able to get in first. I do wonder if his clones would have a wand if he were to create them when he doesn't have the wand (he doesn't always require it to make clones) though...
The idea of him saying "lemme borrow that real quick" is pretty funny! I guess relying on clones can be risky, as
they tend to disappear when
he gets hit, or
get one-shot themselves (seemingly needing
aid from Kamek's wand anyway to survive longer), meaning the wand may disappear alongside them should either be attacked, though I suppose we already covered how he has other means to recover anyway.
Kamek can pretty easily keep Luma's away with any troops he summons. He can also
summon a lot more troops than Rosa and can easily outnumber her summoned Luma's and keep them away from him. He can also just avoid the Luma's with his teleportation and transmute them into more troops with his magic.
Yeah, I do think Kamek has his means of avoiding Lumas, I covered a few means myself, and his own summons would be good at keeping them busy (potentially having Rosalina and the Lumas show off moves against them that Kamek can then take away from them!), but a quick or offguard catch should hold him. Maybe Giant Kamek wouldn't be as easy to paralyse, though
many Lumas working together to stun things seems to be very efficient! Whilst Kamek can summon many minions at once, he doesn't necessarily outnumber her Lumas, as
she can make it rain down Lumas (probably adviced to do towards the start in such an intense battle where Kamek is giving it his all, to not risk him disabling her use of the wand before then!), which should give them roughly even numbers? I'm not too sure if his transmutation would work on Lumas, as one of their big gimmick is their transformative/shapeshifting property, even
readily transforming into Launch Stars and
likely coming back to normal after, which should allow them to transform back if they don't have the same immunity as other cast members. The vase spell from Island Tour could be particularly effective for Kamek, though, as it would likely suck up Rosalina and her Lumas, bringing them all to one place, which at least keeps Rosalina's team on their toes rather than being able to achieve a spread out army effort.
You definitely bring up some good points for Kamek, and sorry if I didn't quite understand where you were going with the first point, but I do still feel even with these tactics in mind, Rosalina can still adapt and provide some of her own counters, even if things can get more and more difficult as the battle progresses and intensifies. I guess since I brought up items, Rosalina and Kamek probably have quite a few effective items they've used throughout their appearances, but nothing much came to mind beyond the ones that also supply Rosalina with item theft (especially since Kamek is able to steal items and disable the use of power-ups in one's inventory considering the Fire Flower and Mega Mushroom are Bros Attacks, so relying on those too heavily may backfire for Rosalina). This match definitely offers a lot of food for thought in how their abilities interact, and still one of my favourites!