Thomas' Adventures of My Little Pony: Friendship is Magic - The Return of Harmony (Full Movie) is an upcoming Thomas & Friends/MLP:FIM Crossover film created by 76859Thomas. It will appear on Google Drive in the near future.
Cheerilee walks her students through Canterlot's sculpture garden, where she shows her class a strange statue of a chimera-like creature known as a draconequus, a creature that represents discord and a lack of harmony. The Cutie Mark Crusaders – Sweetie Belle, Apple Bloom, and Scootaloo – get into a fight over exactly what the statue represents. Soon, the statue begins to mysteriously pulse, though no pony notices at the moment. As the group moves away from the statue, small cracks appear along its surface and an evil chuckle is heard.
Later, Twilight and her best friends Applejack, Fluttershy, Pinkie Pie, Rainbow Dash, and Rarity find strange phenomena occurring around Ponyville, such as cotton candy clouds dispensing chocolate milk, ears of corn in their husks instantly turning into popcorn, and Applejack's apples turning bigger. However, Twilight's magic is not strong enough to stop it, though they can get some of the phenomena somewhat under control. Soon, Spike coughs up a letter from Celestia, urging Twilight and her best friends to see her in Canterlot. On arrival, Celestia takes them to a grand hall with stained-glass windows, including one heralding the ponies' defeat of Nightmare Moon, and to the vault where the Elements of Harmony are kept. Celestia tells the ponies that the strange phenomena they have noticed is being caused by an old enemy of hers named Discord, the spirit of chaos and disharmony. Celestia tells of how Discord once ruled Equestria in an eternal state of chaos before she and Luna defeated him by turning him into a stone statue (the Draconequus statue that stood in the sculpture garden). But he has recently escaped his prison and Celestia asks Twilight and her best friends to use the Elements of Harmony (as they previously did to defeat Nightmare Moon) to defeat Discord. However, as she offers the Elements to them, they are shocked to find that the box that normally holds the Elements is completely empty.
Suddenly, an image of Discord on the stained-glass windows comes to life, teasing the ponies and Celestia. Discord claims to have taken the Elements and alludes to where they can be located. Twilight believes Discord is referring to the hedge maze near the castle and the six race there. Discord appears in his true form and challenges the ponies to a game, telling them that the only rules are they are not allowed to fly or use magic (enforcing this rule by making the unicorns' horns and Pegasi's wings vanish), and that if any of them leave the game, he automatically wins. Despite their handicap, the ponies enter the maze, but they are soon separated by Discord's magic. He is able to individually test Applejack, Pinkie Pie, Rarity, and Fluttershy against their respected Elements, making them be momentarily hypnotized, lose some of their color, and become a polar opposite of their Element. Twilight encounters each of them after this point, aware of their personality shift, but oblivious to their encounter with Discord. Soon, they find Rainbow Dash, having regained her wings, flying away from the maze and betraying not only her Element of Loyalty, but also forfeiting the game by leaving; the maze falls around them and Discord boasts his victory, warning of an incoming storm of chaos.
Twilight confronts Discord, accusing him of cheating since he destroyed the labyrinth before they could get to the end of the game. However, Discord counters this by reminding her that, while he had hinted at where the Elements were, he never said anything about them being in the labyrinth. As he disappears and teases the ponies with another storm of chocolate rain, Twilight realizes that a line from Discord's riddle actually refers to Ponyville itself.
Determined and with renewed hope, Twilight leads her best friends back to Ponyville, which Discord has altered in a chaotic manner: The day-night cycle is haphazard and buildings float off the ground. Discord continues to taunt Twilight, but she is determined to get back to the library in town to find a way to defeat Discord while her best friends' personalities continue to become more warped, losing even more of their color until they are completely monochrome. Managing to get them all into the library, Twilight and Spike locate the book about the Elements of Harmony and after a brief scuffle with the other ponies over the book, are surprised and delighted to find the book actually contains the Elements. She forces her best friends to wear the Elements, though they are more willing to help after she angrily states that the sooner they defeat Discord, the sooner they never have to see each other again; Twilight also assigns Spike as the temporary Element of Loyalty because Rainbow Dash is not present. They go to face Discord, but the Elements fail to activate. The other four ponies and Spike quickly drop the elements and depart, leaving Twilight despondent and finally losing her own color.
Twilight sadly returns to the library, preparing to pack and leave Ponyville, when she finds Spike coughing up scroll after scroll. Twilight is surprised to find these to be the friendship report letters that she had previously sent to Celestia, and the memories of her friendships in Ponyville make her regain her color. Inspired by this, she returns to her other four best friends and uses a memory spell to remind them of their friendship, cancelling Discord's magic and returning them to normal.
However, Rainbow Dash is still apart from the group and without her, the Elements will not activate. They find Rainbow Dash protecting a cloud, believing it to be her home of Cloudsdale. They start to give chase, but Rainbow flies away. They quickly use a hot-air balloon, pulled along by Fluttershy, to catch up to Rainbow. At first, it seems that Rainbow has the upper hand, but as soon as Twilight reminds Fluttershy that if she gets away Discord will win, Fluttershy puts on an enormous burst of speed and the ponies eventually catch Rainbow and manage to tie her down long enough for Twilight to cast her memory spell. The ponies share a hug before remembering that Ponyville is still under Discord's influence.
The ponies collect the Elements and re-approach Discord, who casually passes off their threat. However, with all six ponies restored, the Elements activate, firing a rainbow-beam of light that engulfs Discord and Ponyville. In moments, Ponyville has been returned to normal and Discord is once again turned to stone. The ponies' victory is celebrated by a large ceremony at Canterlot, led by Celestia, who praises their heroism and the power of their friendship and reveals a new stained-glass window of the six ponies defeating Discord.