I feel like people tend to just get scared by Rosalina more than anything. Luma Warp and Shooting Star Bit are pretty much designed to make hanging back not doing much active against Rosalina a pretty terrible tactic. She can harass you with the star bits, she controls the spacing since she's the one who isn't scared to move around, and she can throw a safe power move via Luma Warp at you at any time. You can play a ranged game against her with those customs, but you had better be someone like Villager with a real plan to do this and not just a player who is scared and is not hitting buttons on account of fear. However, if you just respect her a whole lot less, you begin to see the downsides...
-Shooting Star Bit is nowhere near as controlling as it seems. People like to compare it to Falco laser, but it's actually the inverse of Falco laser nearly completely. Falco laser was always a passable grounded harassment tool that became ridiculous when used in the air. Rosalina's SSB is a pretty good grounded harassment tool that becomes honestly flat out bad when used from the air. Luma's position locks during the start-up of the move (unlike Falco's gun that continues to fall with Falco); that means that Rosalina falling and sniping specific spaces with star bits is a lot slower and more awkward than shooting the same things with Falco. SSB also fully commits both Rosalina and Luma for the entire animation without any early way out for either other than getting hit, and it leaves the duo at substantial frame disadvantage on block in most situations so it's almost always unsafe to use at close range and often loses ground when used against a shield at longer ranges. Just walk forward and powershield, and you'll be in before you know it if she's seriously going to spam it. It's also not transcendent like a laser; SSB can be hit out of the air, and it's not even very high priority (Sonic clashes with it while spinning around, for instance). It's still a good move and all for harassment purposes and helping her break extremely defensive opposing strategies, but the hype is overblown.
-Luma Warp as an offensive threat is pretty much predicated on the concept that Rosalina controls the spacing. This should not happen uncontested. Rosalina's mobility is all around mediocre; it's not awful, but most characters can move faster than her. Luma Warp goes the same distance every time and has some amount of start-up; know what that range is, play footsies, and dance around it. If your character is not Ganon or someone like that, you can move fast enough to do this (and if it is Ganon or another slowpoke, you probably have tools that can kill Luma really fast at least). Believe me from the Rosalina perspective whenever I try to tag someone with Luma Warp and they actually just ran in past Luma it's a really bad time. Now Luma is way over there while this unkind character is right up in Rosalina's face. Even if they are on the other side from from Rosalina, it's not as bad, but most characters have some move that can just bop Luma if I sent it out alone and unsupported like that. I watch dabuz just hit people with this a lot and I dunno how he does it other than getting into the other guy's head; those Luma Warp snipes are him making hard reads which speaks more to him being a really good player than the move being overpowered. Like Luma Warp is still an amazing move since it lets me move Luma around and generally actually play actively with two characters which is awesome (default Luma Shot is just so slow), but it's not broken or anything even close to that since every character in the game has substantial counterplay against it.
To speak specifically about Sheik vs Rosalina since it came up, Penetrating Needles are really obnoxious. They pierce through Luma, and the massive shield damage makes it intolerable for Rosalina to block many of them. They're a really big upgrade over default needles in this MU for Sheik. Skimming Grenade is also a move that is pretty much designed to be a middle finger to Luma; Luma can't spotdodge or block, it's really easy to hit wherever you wan with Skimming Grenade, and it often kills Luma so I have to be really smart not to let Luma end up in positions you can snipe it that way. I actually think the customs help Sheik in this match-up a bit more than Rosalina since for all the extra ability I get to utilize Luma you get more ability to negate Luma, but it's still super competitive either way and is IMO a really great match-up just from the perspective of someone who enjoys playing the game competitively.
-Shooting Star Bit is nowhere near as controlling as it seems. People like to compare it to Falco laser, but it's actually the inverse of Falco laser nearly completely. Falco laser was always a passable grounded harassment tool that became ridiculous when used in the air. Rosalina's SSB is a pretty good grounded harassment tool that becomes honestly flat out bad when used from the air. Luma's position locks during the start-up of the move (unlike Falco's gun that continues to fall with Falco); that means that Rosalina falling and sniping specific spaces with star bits is a lot slower and more awkward than shooting the same things with Falco. SSB also fully commits both Rosalina and Luma for the entire animation without any early way out for either other than getting hit, and it leaves the duo at substantial frame disadvantage on block in most situations so it's almost always unsafe to use at close range and often loses ground when used against a shield at longer ranges. Just walk forward and powershield, and you'll be in before you know it if she's seriously going to spam it. It's also not transcendent like a laser; SSB can be hit out of the air, and it's not even very high priority (Sonic clashes with it while spinning around, for instance). It's still a good move and all for harassment purposes and helping her break extremely defensive opposing strategies, but the hype is overblown.
-Luma Warp as an offensive threat is pretty much predicated on the concept that Rosalina controls the spacing. This should not happen uncontested. Rosalina's mobility is all around mediocre; it's not awful, but most characters can move faster than her. Luma Warp goes the same distance every time and has some amount of start-up; know what that range is, play footsies, and dance around it. If your character is not Ganon or someone like that, you can move fast enough to do this (and if it is Ganon or another slowpoke, you probably have tools that can kill Luma really fast at least). Believe me from the Rosalina perspective whenever I try to tag someone with Luma Warp and they actually just ran in past Luma it's a really bad time. Now Luma is way over there while this unkind character is right up in Rosalina's face. Even if they are on the other side from from Rosalina, it's not as bad, but most characters have some move that can just bop Luma if I sent it out alone and unsupported like that. I watch dabuz just hit people with this a lot and I dunno how he does it other than getting into the other guy's head; those Luma Warp snipes are him making hard reads which speaks more to him being a really good player than the move being overpowered. Like Luma Warp is still an amazing move since it lets me move Luma around and generally actually play actively with two characters which is awesome (default Luma Shot is just so slow), but it's not broken or anything even close to that since every character in the game has substantial counterplay against it.
To speak specifically about Sheik vs Rosalina since it came up, Penetrating Needles are really obnoxious. They pierce through Luma, and the massive shield damage makes it intolerable for Rosalina to block many of them. They're a really big upgrade over default needles in this MU for Sheik. Skimming Grenade is also a move that is pretty much designed to be a middle finger to Luma; Luma can't spotdodge or block, it's really easy to hit wherever you wan with Skimming Grenade, and it often kills Luma so I have to be really smart not to let Luma end up in positions you can snipe it that way. I actually think the customs help Sheik in this match-up a bit more than Rosalina since for all the extra ability I get to utilize Luma you get more ability to negate Luma, but it's still super competitive either way and is IMO a really great match-up just from the perspective of someone who enjoys playing the game competitively.