Thomas' Adventures of My Little Pony: Friendship is Magic - Princess Twilight Sparkle (Full Movie) is another upcoming Thomas & Friends/MLP:FIM Crossover film to be created by 76859Thomas. It will appear on Google Drive in the near future.
Twilight Sparkle struggles to adjust to her new wings and duties as a princess while she prepares for the Summer Sun Celebration away from her friends. Shortly after consoling Twilight that night, Princess Celestia is attacked by a black vine. Twilight awakens the next morning to find that Celestia and Luna have disappeared, leaving the sun and moon hanging in the sky, now split between day and night. In addition, the castle guards inform her of an overgrowth of black plants from the Everfree Forest near Ponyville. Returning to Ponyville to gather the Elements of Harmony, Twilight and her friends suspect Discord is responsible and summon him for answers, but he professes innocence. The ponies consult Zecora who, having abandoned the forest, gives Twilight a potion she says will help her learn what is causing the havoc. After drinking the potion, Twilight finds herself in an unfamiliar castle with Princess Luna, who transforms into Nightmare Moon.
Twilight realizes that Luna's transformation is a vision of the past caused by Zecora's potion. Further flashbacks allow her to witness Celestia and Luna's discovery of the Elements of Harmony at the mystical Tree of Harmony in the Everfree Forest. Twilight and her friends enter the forest with the Elements, believing the tree to be in danger. Twilight is soon sent away by her friends as they grow concerned for her safety, but rejoins them after Discord mocks her for putting herself before her friends. Finding the tree entangled by evil vines, Twilight deduces that it needs the Elements to survive and returns them to the tree, eradicating the plants and freeing the princesses. The tree then sprouts a flower containing a chest with six keyholes, mystifying the ponies. Back in Ponyville, Discord admits to sowing the evil plants shortly before his original defeat in a delayed plot to plunder the tree's magic; he claims to have deliberately withheld this so Twilight would learn how to be a proper leader. The Summer Sun Celebration then commences, with Twilight participating before her cheering friends.