Rosalina was mentioned by Luma, who said that "Mama" (referring to Rosalina) was coming to Earth in order to help in the war against the Akatsuki. However, by the time Rosalina arrives, the Akatsuki had been defeated, although she had arrived just in time for the war against Yami Bakura. Despite her Luma advisor, Polari's objections, Rosalina stated she promised to help the Heroes of Legend in their struggle, and even if the opponent has changed, she must keep her promise. Rosalina is soon attacked by Yami Bakura, who desires the power of the Lumas for himself, but is saved by Boo Rock, Gigadark Bowser, and the Heroes of Legend. Later, Rosalina witnesses the Heroes of Legend sacrifice themselves in an attempt to stop Yami Bakura. However, Rosalina is blasted in the gut by Yami Bakura upon his return, resulting in her death. Rosalina is revived after Yami Bakura is defeated. In Season 25, Rosalina is mentioned by Luma again, who said that he was sent to help Mario. Rosalina is later seen watching as Universe-616 begins to destabilize, and flees to Earth-T with everyone else. Later, Rosalina participates in the fight against the Nomadic Mechtogan alongside her friends. Following this, Rosalina later battles alongside her friends against the Nomadic Mechtogan once again, but is left behind when they are forced to retreat, and is nearly possessed by Coredegon, but for some unknown reason, Coredegon splits Rosalina into multiple copies of herself and absorbs her negative energy. This is later exploited in Season 29, where Coredegon revives himself through the DNA he left in Rosalina, and Rosalina is subsequently possessed by Coredegon. However, Rosalina is subsequently released when Coredegon gives every fighter a Smash Core fragment, but is still under Coredegon's influence. In Season 32, Mechtavius Destroyer reveals that during his failed attempt to possess Rosalina, he left a seed within her subconscious, effectively making her a sleeper agent. Mechtavius Destroyer then proceeds to fuse Rosalina with Zero Two for the final battle against the Heroes of Legend. However, Galacta Knight purges Zero Two from Rosalina, but the exposure to the source of Dark Matter ultimately causes Rosalina to go insane, prompting the Heroes of Legend to have Rosalina removed from the fight against the Skrulls so she can regain her sanity. Unfortunately, Zombie Giant-Man, having come to view the Earth as corrupted, gives some of his Power Cosmic to Rosalina to keep her mentally unstable as proof of his views. Rosalina is subsequently convinced to help Mechtavius Destroyer end all life on Earth. Following Mechtavius Destroyer's defeat, Rosalina is given a modified version of Samus Aran's Metroid buzzers by Zombie Giant-Man so she can absorb energy herself, unaware that Zombie Giant-Man is still manipulating her. Following Zombie Giant-Man's defeat, Rosalina is removed from the Earth once again in the hopes that her sanity will return. However, Rosalina begins to question her identity, due to how she felt when Princess Peach was restraining her, describing it as "a mother restraining her unruly child". Rosalina then jumps down to Angel Island, threatening Knuckles the Echidna to get the Heroes of Legend to her. However, the Heroes of Legend arrived regardless, causing a conflict between the Heroes of Legend, Knuckles, Rosalina, Tikal, and Scourge the Hedgehog. However, the Heroes of Legend flee, and Rosalina begins questioning her identity once again when Coredegon approaches her, and tells her how she was flung into the past by Solaris during his rampage, which somehow altered her DNA, and informs her that Sonic the Hedgehog, Shadow the Hedgehog, and Silver the Hedgehog failed to stop Solaris in time. Furious at how her life was ruined because of the hedgehogs, Rosalina declares vengeance on them and the Earth for setting her soul free. It is later revealed that Rosalina is indeed from the future and is the daughter of Mario and Peach after they receive a baby that looks like Rosalina. After Mechtavius Destroyer is defeated, Rosalina begins to question her identity once again after discovering from Sonic that she is indeed Peach's daughter. It is subsequently revealed that Rosalina revived Master Hand to acquire these answers. Rosalina then learns that the alteration Coredegon told her about was a part of Master Hand's soul being transferred into her, which is the source of her immortality. Rosalina is then offered by Master Hand to train under him. Still mentally unstable and determined to learn her identity, Rosalina agrees to let Master Hand train her, apparently unaware he intends to use her as a weapon. Rosalina doesn't reappear until the conflict against Dr. Eggman, where she has completed her training under Master Hand before a Luma informs her of the crisis through a news report on television. Upon hearing Master Hand let out an evil laugh, Rosalina electrocutes him, revealing that she knew he was using her and that laugh confirmed it. Rosalina then mocks Master Hand for creating a weapon he couldn't control before knocking him out. Rosalina then proceeds to go to the Egg Carrier, but removes Dr. Eggman's Egg Destroyer armor so he couldn't kill the Heroes of Legend. Upon arrival, Rosalina teleports Dr. Eggman away, and reveals to the heroes and villains her recent activity and origins before declaring her intent to usurp the Heroes of Legend as the Creator. Rosalina then proceeds to summon every evil creature in existence and ressurects Male, Female, and Giga Bowser, as well as having Jen ressurect the creepypastas that Sonic erased from existence. Rosalina then tops it off by reviving Zero Two, and declares she will not make the same mistake Master Hand made by ensuring that everyone dies in front of her. Despite the Heroes of Legend being exhausted from their fight with Dr. Eggman, Rosalina is defeated after the Crystal Stars and the Chaos Emeralds revitalize the Heroes of Legend with the energy of everyone from every dimension. Rosalina is then stripped of her Dark Matter generating powers by Zombie Iron Man, and her Metroid buzzers are destroyed by Samus Aran. Rosalina later temporarily teams up with the heroes and villains to fight Mechtavius Destroyer, but betrays them after witnessing the power of the Dark Star first hand, and absorbs Dark Bowser to increase her strength and become the new Creator. Rosalina then proceeds to absorb Zero Two to become complete. However, Rosalina is stripped of her enhanced power after Gohan punches her so hard that she vomits up Fawful, who has become the Dark Star's Core, resulting in Gohan pulling the Dark Star out of Rosalina. Rosalina then loses Zero Two's power after Mario purges Zero Two from her body by using the Master Sword. However, Rosalina refuses to lose again, and says that she will annihilate all the dimensions and those who inhabit it, before rebuilding it as she sees fit. However, after the Heroes of Legend are declared the Rulers of the Dimensions and witnessing Fawful's brutal defeat, Rosalina realizes she cannot defeat the Heroes of Legend with her current power. However, Ganondorf approaches Rosalina and offers her membership with the Heroes of Legend so that she can help them make a new world. Unable to win with her current power, Rosalina reluctantly joins the Heroes of Legend. Rosalina later learns after reading the Dark Prophecy that Master Hand created Solaris. After Shadow the Hedgehog teleports the others back to Smash City, Rosalina asks if she is going to be arrested now, but is shocked when Shadow says that they weren't going to arrest. Rosalina then states that she caused the Heroes of Legend so much trouble and betrayed them, but Vegeta reminds Rosalina that Master Hand manipulated everyone and that it isn't her fault. Relieved, Rosalina finally rejoins the side of good.
Rosalina looks similar to Princess Peach, but with some noticable differences. Rosalina's crown is silver instead of gold, her sleeves are longer than Peach's, and there is no waist area on Rosalina's dress.
After being fused with Zero Two, Rosalina wears an outfit similar to the one Peach wore when she was possessed by the Shadow Queen. In addition, Rosalina's hair becomes white, her eyes become the same color as Zero Two's eye, and gains Zero Two's wings.
After Zombie Giant-Man gives her some of his Power Cosmic, Rosalina wears the Galacti uniform.
Following her decision to get vengeance on the Earth, Rosalina wears a dark version of her usual outfit.
During her training under Master Hand, Rosalina wore a white version of her usual outfit.
After absorbing the Dark Star, Rosalina's outfit becomes similar to that of Dark Fawful's outfit. In addition, her irises' become the same as Fawful's glasses. Upon absorbing Zero Two, Rosalina regains Zero Two's wings.
Despite the fact that she rarely displayed any emotion, Rosalina was kind and caring about her friends before being driven insane. Rosalina has a special bond with the Lumas, and displays genuine anger when anyone tries to kill them. This bond remains intact following Rosalina's descent into madness.
Following the absorption of negative energies during her time on Earth, Rosalina has ultimately lost her sanity and desires more power due to the feeling it provides her. In addition, Rosalina also shows bitterness towards her friends due to being convinced they abandoned her to die at Mechtavius Destroyer's hands. This hatred is only intensified due to Coredegon's manipulations. By the time she finished her training with Master Hand, Rosalina has lost all traces of her sanity, and is now convinced she is meant to become the new Creator. However, after Rosalina learns the truth about Master Hand's creation of Solaris, she realizes that she was wrong to betray her friends, and was willing to be arrested out of guilt for her crimes.