Thomas and Twilight Sparkle's Adventures of Justice League

Thomas and Twilight Sparkle's Adventures of Justice League is the first upcoming Thomas & Friends/MLP:FIM/Justice League crossover to be made by Hiatt Grey.

Plot
Thousands of years ago, Steppenwolf and his army of Parademons attempt to conquer and remake Earth through the combined energies of the Mother Boxes. They are foiled by a unified army that included the Olympian Gods, Amazons, Atlanteans, ancient humans, and Green Lanterns. After repelling Steppenwolf's army, the Mother Boxes are separated and hidden in locations around the world.

In the present, the death of Superman triggers the Mother Boxes to activate, resulting in Steppenwolf's return to Earth in an effort to regain favor with his master, Darkseid. Steppenwolf manages to retrieve the Mother Box from Themyscira, prompting Queen Hippolyta to warn her daughter, Diana Prince, of Steppenwolf's return. Diana joins Bruce Wayne in his attempt to unite the other metahumans, with Wayne going after Arthur Curry and Barry Allen, while Diana tries to locate Victor Stone. The two of them fail to persuade Curry and Stone, but manage to recruit Allen onto the team. Stone later joins the group after his father Silas is kidnapped, along with several other S.T.A.R. Labs employees, by Steppenwolf who is looking for the box left with mankind.

Meanwhile, Steppenwolf attacks Atlantis to retrieve the second Mother Box, forcing Curry to decide to take action. The team receives intel from Commissioner James Gordon that the Parademons are traveling underground, and conclude that Steppenwolf's army is based in an abandoned facility. Although the group manages to rescue the kidnapped employees, the facility is flooded during combat, which traps the team until Curry helps delay the flood so they can escape. Stone retrieves the last Mother Box, which he had hidden, for the group to analyze. Wayne decides to use the Mother Box to resurrect Superman, not only to help them fight Steppenwolf's army, but also to restore hope in humanity. Prince and Curry are hesitant about the idea, but Wayne forms a secret contingency plan in case Superman returns as a nemesis.

Clark Kent's body is exhumed and placed in the incubation waters of the Kryptonian ship alongside the Mother Box, which activates with Allen's help and successfully resurrects Superman. However, Superman's memories have not returned, and he attacks the group after Stone accidentally launches a projectile at him. On the verge of being killed by Superman, Batman enacts his contingency plan: Lois Lane. Superman calms down and leaves with Lois to his family home in Smallville, where he reflects and tries to recover his memories. With the last Mother Box unguarded, Steppenwolf retrieves it with ease.

Without Superman to aid them, the remaining five heroes travel to a village in Russia where Steppenwolf plans to unite the boxes once again and reshape the world. The team fight their way through the Parademons to reach Steppenwolf, although they are unable to distract him enough for Stone to separate the boxes. Superman arrives and assists Allen in evacuating the city, as well as Stone in separating the Mother Boxes. The united heroes manage to defeat Steppenwolf, who, overcome with fear, is attacked by his own Parademons, before they all teleport away.

In the aftermath of the battle, Wayne and Diana agree on the decision to rebuild Wayne Manor as a base of operations for the team, with additional space for more heroes in the future. Prince steps back into the public spotlight as a hero; Allen manages to acquire a job in Central City's police department; Stone continues to explore and enhance his abilities with his father in S.T.A.R. Labs; Curry returns to Atlantis; and Clark resumes his role as Superman. In the post-credits scene, Lex Luthor has escaped from Arkham Asylum and recruits Slade Wilson to form their own league.

Trivia

 * Knockout, Puffer, Dolphy, Rachel, Mighty Joe, Jenny, Pete, Kevin, Morley, Blitzer, Spencer, Duck, Donald and Douglas, Oliver, Toad, Button Mash, Babs Seed, Team Griffin/Eeveelution Family, Peter Griffin, Glenn Quagmire, Cleveland Brown, Joe Swanson, Vinny Griffin, Blythe Baxter, Zoe Trent, Gail Trent, Pepper Clark, Penny Ling, Sunil Nevla, Vinnie Terrio, Minka Mark, Russell Ferguson, Mitzi, Buttercream Sunday, Sugar Sprinkles, Dudley Puppy, and Kitty Katswell guest star in this film.
 * The storyline continues in Thomas and Twilight Sparkle's Adventures of Justice League Dark.