Ed, Edd n Eddy in Equestria Girls: Rainbow Rocks

Ed, Edd n Eddy in Equestria Girls: Rainbow Rocks is a crossover film of Ed, Edd n Eddy and My Little Pony: Equestria Girls - Rainbow Rocks. It's the sequel to Ed, Edd n Eddy in Equestria Girls, and followed by Ed, Edd n Eddy in Equestria Girls: Friendship Games.

Prologue: Equestrian magic
The film opens at a café in the human world. The numerous café patrons argue among themselves as a strange green mist swirls around their feet. In the corner booth, three girls in hoods sing and absorb the green mist into the red gems on their necklaces. The purple-haired girl Aria Blaze grumbles that she's "tired of fast food" and needs a meal. The orange-haired girl Adagio Dazzle laments that the energy in "this world" isn't the same as that in Equestria.

As the blue-haired girl Sonata Dusk joins the conversation and gets into a light argument with Aria, Adagio notices an explosion of light in the distance. She races out of the café and watches the magical rainbow energy burst into the sky, grinning evilly when she realizes what it is. She explains to Aria and Sonata that Equestrian magic has found its way into the human world, and they're going to use it to make everyone adore them.

Sunset Shimmer's efforts
Six moons[16] later, at Canterlot High School, the students are busy making banners in the auditorium for the school's upcoming musical showcase. Sunset Shimmer offers to help the Cutie Mark Crusaders with their banner, but they decline, much to Sunset's disappointment. When Pinkie Pie and Ed call Sunset over to join her and her friends, the other present students glare at and gossip about Sunset, making her uncomfortable. Rarity and Edd (aka Double D) quickly change the subject and shows Sunset the banner they made for the showcase (which Pinkie and Ed used cake frosting on instead of paste).

Principal Celestia and Vice Principal Luna then enter, and Celestia says how pleased she is by the amount of student participation in the showcase. However, when she mentions the Fall Formal, the students glare at Sunset again and Sunset hides her face in humiliation.

Later, in the school band room, Sunset laments how she'll never live her past mistakes down. Her friends, now in an eight-part band called the Rainbooms, say they've forgiven her and cheer her up with a rehearsal of Better Than Ever. As they sing, the eight bandmates sprout pony ears and wings and longer hair, which disappear when they stop playing. Rarity, Applejack and the Eds express disbelief at the strange phenomenon, but Rainbow Dash cares little, letting her band leader egotism show.

Flash Sentry enters, having heard the band's playing from outside the room, and compliments their sound. When Rainbow criticizes Rarity and Applejack's playing, they give an annoyed look. Flash asks if "any friends from out of town" will be coming to the showcase. The Rainbooms tell him they're not sure if Twilight will be present, and Flash awkwardly excuses himself. Rarity and Edd are amused by Flash's behavior, but they stop themselves when they remember that they and Sunset used to date. Sunset admits that she never liked Flash romantically and further regrets her past actions. As Applejack cheers them up, a speaker announcement by Vice Principal Luna summons Sunset Shimmer to the school foyer. Sunset leaves the room, having promised to give a tour to some new students and the Rainbooms go back to rehearsing. Fluttershy asks if they can sing a song she wrote, to which Rainbow Dash and Eddy reply that they'll get to it later.

Enter the Dazzlings
At the school entrance, Sunset Shimmer meets with the new girls - Adagio, Aria, and Sonata - and shows them around the school. During the tour, they pass by a flyer for Canterlot High's musical showcase; Sunset talks about the event, and the girls are intrigued, with Sonata nearly revealing their true nature. When Sunset notices the three's gem necklaces and reaches for Adagio's, Adagio grabs Sunset's wrist in sudden offense. Adagio catches herself and apologizes, explaining that their pendants mean a lot to them and they don't want anything to happen to them. The three girls walk off, leaving Sunset to ponder their strange behavior.

Later in the cafeteria, Sunset joins her friends and mentions that there is something "off" about the new girls, worrying that they know about the events of the Fall Formal. Outside the cafeteria doors, Adagio, Aria, and Sonata have a brief argument before they enter. With their beguiling voices and a rousing song, the girls convince the students of Canterlot High to turn the musical showcase into an all-out Battle of the Bands. As they sing, tensions rise among the students, causing them to argue. As each vows victory in the competition, green mist forms around them, which Adagio, Aria, and Sonata absorb into their pendants. Only Sunset Shimmer and her friends are unaffected by the song.

A mesmerized school
Sunset Shimmer and the Rainbooms suspect that Adagio, Aria, and Sonata are using dark magic on the students and go to alert the principals. However, Celestia and Luna believe the girls, now calling themselves the Dazzlings, are innocent and even praise them for their Battle of the Bands idea. For a brief moment, the principals' eyes glow green, indicating that they have also fallen under the Dazzlings' spell.

The Rainbooms deduce that the magic that causes them to transform while playing music also makes them immune to the Dazzlings' spell. With the rest of the school under the Dazzlings' control, the friends consider getting Princess Twilight to return and help. The closed portal prevents her from returning, but Sunset Shimmer has an idea. In her locker, she finds an old book with her cutie mark on the cover and explains that she used it to write messages to Princess Celestia, which would appear in a book in Celestia's library. Hoping to get a message to Princess Twilight, Sunset opens the book and begins to write, starting with the three words she hadn't written in a long time...
 * "Dear Princess Celestia..."
 * — Sunset Shimmer

Back in Equestria
In Ponyville, at the Castle of Friendship, Twilight and her friends lounge about in the throne room when a stallion arrives with a delivery of books from Princess Celestia. One of the books, with Celestia's cutie mark on the cover, appears to glow and vibrate. Twilight opens it and discovers Sunset's call for help.

Twilight determines from Sunset's warning that the Dazzlings are actually Equestrian sirens. Long ago, the sirens used their eerie songs to turn ponies against one another and fed on the negative energy from their hatred and distrust, which made them powerful enough to control minds. But before they could conquer Equestria with their magic, Star Swirl the Bearded banished them to another world—the world where Sunset Shimmer now lives with the human counterparts of Twilight's Ponyville friends and the Eds.

Twilight wishes to go and help her human friends, but the Crystal Mirror's closure prevents her from doing so. Pinkie Pie proposes that the same magic that allows Sunset Shimmer to send messages from the human world to Equestria should allow the portal to be opened. With a bunch of mechanical parts, and using the book as a battery, Twilight is able to energize and reopen the portal. Her friends want to accompany her, but Twilight tells them they can't because it would be confusing to have two copies of her friends in the same place. Spike can still go along, however, and he and Twilight soon charge into the portal.

Return to Canterlot High
Back at the school, Rainbow and Eddy start to lose hope that Twilight will come, when Twilight and Spike suddenly shoot out of the portal. Her human friends meet her in a group hug (especially Ed). Later at Mr. and Mrs. Cake's Sweet Shoppe, the friends all catch up, with Spike revealing Twilight's  new status as the Princess of Friendship. Once Twilight learns of what they're up against, she comes up with a plan to ambush the Dazzlings at the pre-Battle of the Bands party being held in the school gym.

At the band meetup, Twilight bumps into Flash Sentry and stammers in his presence. Once the Dazzlings arrive, Twilight and her friends declare their evil plans finished and attempt to stop them with a magic of friendship attack. However, nothing happens, allowing the Dazzlings to feed on even more of the competitors' negativity. Having humiliated themselves, Twilight and her friends excuse themselves, but the Dazzlings decide to keep an eye on them, calling them "special".

Twilight and the others regroup outside the school and try to figure out what went wrong. They reason that, since they can only channel their magic when playing music, only a counter-spell in the form of a song will break the Dazzlings' spell, making the Battle of the Bands the perfect venue. They also decide Twilight should be the Rainbooms' new lead singer, much to Rainbow Dash and Eddy's chagrin. Before Twilight retires to the school library like she did during her last visit to Canterlot High, Pinkie Pie and Ed propose a slumber party at Pinkie's house.

That evening, as her friends enjoy themselves around her, Twilight has considerable difficulty writing a counter-spell. Later, after everyone falls asleep, she works on it in the kitchen and is soon joined by Sunset Shimmer. As the two bond over the similar problems they each face, Sunset is startled when Pinkie's sister Maud comes in to get a snack for Boulder.
 * "I still can't get over the fact that she's related to Pinkie Pie."
 * — Sunset Shimmer

The next day, the Rainbooms practice their musical counter-spell in the barn next to Applejack's house. Unfortunately, Twilight's singing is so off-key that Rainbow Dash and the Eds only manage a small bit of transformation. Before long, hostility continues to grow between the Rainbooms regarding Rarity's costumes and Rainbow's insisting that the band is hers. With the Battle of the Bands starting soon, the Rainbooms soon agree to perform other songs and stall for time until Twilight can complete her spell. In addition, they decide to keep their magic a secret from the Dazzlings for as long as possible.

The Mane Event
The Battle of the Bands gets underway, with Snips and Snails performing a hip-hop duet that earns only confused looks from the audience and reprimanding from Principal Celestia when they drop the microphones. When the time comes for the Rainbooms to perform, Rarity and Edd take the stage in a hippie-inspired outfit with metal fringes. During their performance of Shake Your Tail, other competitors try to sabotage them: Photo Finish and the Snapshots manipulate Rarity's movement with a magnet, and Snips and Snails take advantage of Fluttershy's stage fright by holding a spotlight over her.

The Rainbooms manage to advance to the next round, but they continue to squabble over petty issues. Later, even Flash Sentry starts to show hostility toward Twilight, considering her to be an enemy because she is on a rivaling band. As they part ways, a heartbroken Twilight walks away in tears. At the other end of the hallway, Sunset confronts the Dazzlings about their evil schemes, but the Dazzlings play to Sunset's fragile emotions and make her feel useless in her friends' eyes.

In the following montage set to the Dazzlings' Under Our Spell, competing bands are eliminated one by one, from the Crusaders to Bulk Biceps to Lyra Heartstrings and Sweetie Drops to even Flash Sentry. In the semifinals, the Rainbooms face Trixie and the Illusions to decide who faces the Dazzlings in the final round.

As Trixie and her band perform Tricks Up My Sleeve, Twilight still has yet to finish her counter-spell song, so Rainbow Dash and Eddy take over as lead singers and the Rainbooms perform Awesome As I Wanna Be. However, Rainbow Dash and Eddy get carried away and start to transform, prompting Sunset Shimmer to leap in and cut the song short. The crowd is convinced that Sunset hasn't changed, adding more fuel to the fire of hatred for the Dazzlings to feed on.

Trixie's dirty tricks
Through the Dazzlings' manipulation of the principals, the Rainbooms advance to the final round instead of the Illusions. An embittered Trixie is later approached by Adagio and given the idea of removing the Rainbooms from the competition so the Illusions can take their place in the finals.

During the Rainbooms' mic check on the stage where the finals are to take place, Trixie and the Illusions arrive to carry out their plan: a lever opens a trap door on the stage, and the Rainbooms fall inside. Spike, the only one not to become trapped, rushes off to find help.

That night, the Illusions perform in the finals following the Rainbooms' supposed forfeit. Afterward, the Dazzlings take the stage for their final performance and continue feeding off the crowd. Below the stage, tempers and tensions finally boil over between the Rainbooms and an eight-way argument breaks out, allowing the Dazzlings on stage to feed on their hatred.

Sunset notices what's happening and finally intervenes, pointing out that their arguing has warped the magic of friendship into something that the Dazzlings can feed on. Twilight is ashamed that she hadn't realized it sooner, and Sunset tells her no one is supposed to have all the answers, but friends can help you find them. The Rainbooms thus make amends and finally come to a compromise, and Spike arrives to rescue them with the help of DJ Pon-3, whose headphones shielded her from the Dazzlings' spell.

Welcome to the Show
The Dazzlings continue feeding on the crowd on stage and transform, giving them pony ears, tails, and translucent wings. As the Rainbooms watch from atop a hill, wondering how their song can reach the crowd, DJ Pon-3 arrives with further assistance: a car that converts into a DJ station. The Rainbooms start to play their counter-spell song over the Dazzlings' song and take on half-pony forms with colors similar to that of the Mane Six and the Eds' Rainbow Power. Refusing to be stopped, the Dazzlings summon astral versions of their true siren forms and manage to overpower the Rainbooms.

As the Rainbooms fall, Twilight's microphone rolls next to Sunset Shimmer's feet, and Twilight says they need her help. Sunset finds new resolve and, upon removing her jacket, starts to sing. Before long, the rest of the Rainbooms join her, and their combined magic creates a rainbow shockwave that weakens the Dazzlings and severs their spell over everyone, much to Adagio's disbelief. The magic of friendship builds inside Sunset, granting her a half-pony form of her own. All the students then join in, and as the Dazzlings look on in shock and horror, the magic coalescing in the sky takes the form of a giant Alicorn that destroys their astral projections as well as their gem pendants.

With their power sources destroyed, the Dazzlings are unable to even sing and re-cast their spell. The enraged students boo, jeer, and pelt them with fruits and vegetables, forcing them to flee in shame and disgrace. Flash, now free of the Dazzlings' influence, meets Twilight in a happy and warm embrace. However, Trixie, still upset about her competition loss, makes it clear she isn't done with the Rainbooms yet. As for Sunset, with Twilight now having to return home to Equestria, Rainbow and the Eds allow Sunset to join the band in Twilight's stead—especially after Sunset reveals she can play the guitar.

Dear Princess Twilight
Before Twilight leaves, she promises to visit whenever she can now that the portal can be opened at any time. Later, as the girls and the Eds tune up their instruments, Sunset uses her old journal to write the friendship lesson she learned to Princess Twilight, ending it with the closing statement:
 * "Your friend, Sunset Shimmer."
 * — Sunset Shimmer

As the film closes, Sunset picks up her guitar and joins her bandmates in a performance of Shine Like Rainbows. During the credits, Sunset is seen having now been accepted by the rest of the school, as the Cutie Mark Crusaders help her with her books and walk with her and Bulk Biceps helps her get Angel down from a hard-to-reach perch.

Epilogue: The other Twilight
In a post-credits scene, the human world's version of Twilight Sparkle is seen documenting strange events that are all connected to Canterlot High. She confides in her dog Spike that "something strange [is] going on at that school..."