The students of Canterlot High School prepare for the Friendship Games, an academic and sporting competition held every four years between their school's team, the Wondercolts, and the undefeated Shadowbolts from Crystal Prep Academy. Sunset Shimmer, who has been observing her friends' magical ability to "pony up" – grow pony-like ears, tails, and wings – whenever they play musical instruments, becomes concerned when Rainbow Dash transforms during a pep rally, seemingly at random. Tasked with finding the cause of this development, Sunset attempts to contact Twilight Sparkle for advice but receives no response. Meanwhile, one of Crystal Prep's students, Twilight's counterpart in the parallel world, investigates the magical activity surrounding Canterlot High. Twilight builds a locket-like device to detect and contain the magic for further study, hoping this will secure her application for Everton, a coveted independent study program. However, Principal Cinch threatens to revoke the application to blackmail Twilight into participating in the Friendship Games and maintain Crystal Prep's victory record. Upon Twilight's arrival at Canterlot High, her device detects Sunset and her friends' magic and leads Twilight to them; as she approaches, the device inadvertently drains Rarity's magic when she "ponies up" after making uniforms for the other girls. Sunset, initially mistaking Twilight for her Ponyville counterpart, quickly realizes the misunderstanding and considers consulting Twilight in person. When Crystal Prep's Twilight follows her to the portal to Equestria, the device absorbs the portal's magic and seals it off. The device similarly affects Pinkie Pie when she tries to ease the tension with a party and later Fluttershy when she attempts to cheer up a distraught Twilight, creating dimensional rifts to Equestria and giving Twilight's dog Spike the ability to speak. Following Twilight's victory in the games' academic decathlon, the games continue with a "tri cross relay", a relay race between archery, speed skating and motocross. Applejack transforms after she advises Twilight, causing the device to steal Applejack's magic and create a rift that summons monstrous plants. Rainbow Dash "ponies up" to save the other competitors before losing her magic, allowing Canterlot High to win the event, but causing Cinch to accuse Canterlot High of cheating due to their perceived magical advantage. Frustrated by her failure to keep the magic protected, Sunset furiously berates Twilight for endangering her friends, regretting it when Twilight runs off in tears. That evening, before the final event, Cinch and the Shadowbolts pressure Twilight into releasing the magic within her device to harness it against the Wondercolts. The magic instead corrupts Twilight, turning her into a winged monster called Midnight Sparkle who proceeds to destroy the statue portal and open more rifts that threaten to destroy the parallel world. As the Wondercolts and Shadowbolts work together to save their classmates, Sunset notices her friends' magical auras and realizes that their magic manifests when they exhibit the same traits as the Elements of Harmony. Gathering their magic with the device, Sunset assumes an angelic form resembling Princess Celestia, called Daydream Shimmer, closes the rifts, and returns Twilight to normal. Refusing to relent from manipulating Twilight, Cinch threatens to report the incident to the school board. When taunted that no one would believe her account of the magical incidents, however, she concedes to a tie that is celebrated by both teams. Reconsidering her Everton application, Twilight realizes she is happier at Canterlot High and transfers there, where Sunset and the other students welcome her as a new friend. In a post-credits scene, Ponyville's Twilight emerges from the portal with the counterparts of her friends gathered around it. She apologizes for her absence, explaining that she has just escaped from a time travel loop, before gawking at the sight of her counterpart.