In another dimension, the villain Devious attempts to take the magical Luna Cat Medallion from Queen Miragina Linehault, but she renounces her claim to the medallion and it seeks out a worthy successor. It makes its way across dimensions and finds itself with Trixie, and she uses the medallion to become the superhero Lady Masquerade. But the power she now has and the thrill of being a hero quickly go to her head.
- Acquired Situational Narcissism: Trixie finally gaining superpowers of her own quickly goes to her head, and causes her to start acting like her old annoying showboating self from before she started hanging out with Flash. Her attitude quickly gets on Flash's and the Rainbooms' nerves.
- Armor-Piercing Question:
- When Flash and the Rainbooms try telling Trixie it will be safer for her to give up the mask and coin since they don't know where it came from or what could happen if she keeps using them, Trixie fires back what they would do if others told them to stop using their geodes because they think something might happen, even if they had no idea what it was. Nobody was able to answer, thus proving her point.
- When Flash complains to Shining Armor over how annoying Trixie is being and is letting the fame go to her head instead of being a true hero, he points out he just goes in and does what he needs to before leaving instead of sticking around for autographs and selfies like she does. Shining points out though that's only because Flash is on a time limit before he transforms back to normal, and asks if he can look him in the eye and say he wouldn't do the same as Trixie if he could stay an alien for as long as he wants. Flash prepares to say yes, but upon thinking about it can't actually bring himself to actually say it.
- Big Damn Heroes: Right when Devious begins draining Trixie's powers from her to gain her medallion, slowly killing her in the process, Diamondhead arrives to save her and the Rainbooms, stopping Devious.
- Bittersweet Ending: Trixie gives up the Luna Cat Medallion to Prince Aareus Saintworthy so he can return it to his kingdom, and Devious is captured and imprisoned in the kingdom for his crimes. Though Trixie is upset over losing her new powers, she is also ashamed of herself for how she acted while having them and apologizes to Flash for her behavior. But Flash forgives her and comforts her, reminding her of all the times she helped save him even without any powers.
- Celebrity Superhero: Deconstructed; Lady Masquerade quickly becomes famous with her heroic deeds around town, but Trixie lets all of this fame and praise go to her head and revert to her old arrogant self. She starts caring more about signing autographs and getting photos taken than just helping people, and she starts acting proud of herself even in her civilian form. When the Rainbooms point out nobody but them and Flash know it is her behind the mask, she arrogantly says maybe she will just reveal her Secret Identity to get more fame.
- Jerkass Realization: Flash coming to Trixie's rescue even while he is annoyed with her recent behavior causes Trixie to realize how selfish she has been acting and that she isn't a real hero like him.
- Licked by the Dog: When Trixie visits Flash to apologize to him for her behavior, Flash's dog Banana rests his head in her lap.
- No-Sell: Diamondhead's body is able to brush off most of Devious' spells, which Twilight explains is due to the high durability of diamonds. The only magic shown to work on Diamondhead is a cloud of darkness that melts the diamonds like acid.
- Only the Chosen May Wield: As Devious explains, the Luna Cat Medallion has a consciousness and whenever the previous wielder either dies or renounces their claim on it, it will seek out a worthy user within that line of succession. After it chose Trixie as its new wielder, the Rainbooms couldn't use it themselves and theorize that only Trixie is capable of using it, similar to their geodes.
- Refuse to Rescue the Disliked: Subverted; Trixie is actually surprised when Flash comes to her rescue against Devious. She knew how annoyed he was at her and figured if she wound up in trouble he would just tell her to fix it herself. This makes her realize Flash wouldn't do that because he's a true hero, unlike her.
- We Will Meet Again: The ending scene has Devious imprisoned in the Luna Cat Kingdom, vowing that he'll get out one day and everyone would be sorry.
