Former Canterlot High School bully and student of
Princess Celestia,
Sunset Shimmer, who has reformed after being defeated by the magic of
Twilight Sparkle's crown, is ostracized by most of the school despite her efforts to atone. Her only friends are the counterparts of
Rainbow Dash,
Applejack,
Pinkie Pie,
Fluttershy and
Rarity, who have formed a rock band called "the Rainbooms" to participate in the school's upcoming musical showcase. The five girls discover that the magic left over from Twilight's crown has given them the ability to grow pony-like ears, tails, and wings when they play their instruments. Hoping to make a fresh impression, Sunset gives a school tour to three new students – Adagio Dazzle, Aria Blaze, and Sonata Dusk – and informs them of the showcase, unaware that they possess magical powers. Calling themselves "the Dazzlings", the trio performs a song that turns the other students aggressive and competitive towards one another, convincing them to turn the showcase into a
battle of the bands. Sunset and her friends are protected from the song by their magic, but fail to convince
Principal Celestia and
Vice Principal Luna of the danger. Sunset remembers a magical book kept by Princess Celestia, her mentor from
Equestria, which she uses to send a message requesting Twilight's help. Receiving Sunset's message, Twilight deduces that the Dazzlings are
sirens from Equestria that feed on negative emotions to fuel their singing powers for their goal of world conquest. Twilight uses the book's magic to reactivate the portal, allowing her and
Spike to return to the parallel world. Twilight and the girls attempt to lift the Sirens' spell, but it takes no effect. Concluding that they must perform a musical counter-spell, the girls enter the battle of the bands to give Twilight time to complete the spell. The Rainbooms face hostility and sabotage from the other bands throughout the competition, which raises tensions among themselves. Desperate for time in the semi-final round against
Trixie's band, Rainbow Dash performs an egotistical song to substitute the counter-spell and unknowingly nearly transforms. Sunset impulsively ruins her performance to keep her from exposing their plan to the Sirens, which angers the girls. The Sirens intervene to allow the Rainbooms' advancement to the final round anyway, which prompts a jealous Trixie to trap the Rainbooms beneath the stage to take their place. The girls enter a five-way argument (Rarity over Applejack not caring about her costume ideas for the band, Fluttershy over Rainbow Dash taking all the credit for the band and not playing any songs that she wrote, and Pinkie Pie because being in the band is not fun), allowing the Sirens to absorb their magic. Realizing that their constant fighting is interfering with the counter-spell, Sunset convinces the girls to resolve their differences, while Twilight reasons that playing together as friends will make the counter-spell work. Spike rescues the girls with assistance from
DJ Pon-3, whose headphones' music protects her from the Sirens' spell. DJ Pon-3 provides a sound system that the Rainbooms use to engage the Sirens in a musical battle after they had reached their peak in the movie with their signature "We will be adored" verse. The Dazzlings use the magic from the Rainbooms' negative energy to gain similar power, including an ear-tail combo, with featherless, transparent wings. The Rainbooms interrupt directly after the Sirens finished their verse, and proceed to transform into their "ponied-up" forms to counter the Dazzlings' spell. The Dazzlings then summon their astral projections and the bands engage in combat with music, and are overwhelmed by the Sirens. They get knocked down by the Dazzlings' power, before being joined by Sunset after Twilight had the microphone flung out of her hand, and with Sunset's help, they destroy the Sirens' pendants and the sources of their powers, leading to the Sirens being booed offstage. Afterward, Twilight and Spike return to Equestria, while Sunset uses Celestia's book to remain in contact with Twilight. During the credits, Sunset is seen having now been accepted by the rest of the school and getting the hiccups. In a
post-credits scene, the
parallel world's version of Twilight, sunset's twin sister, is shown investigating the strange magical activity around Canterlot High School, remarking that "something strange" is going on there. ==Cast==