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. you are a new CHS student named Zar and you have strange Powers but your a red and purple hedgehog and you have your brother sonic the hedgehog.