2023.

Ten years ago, a mysterious comet struck New York City, spreading an alien toxin across the planet, leaving buildings unharmed, but killing most human and animal life on Earth, putting the world in a state of crisis and pandemonium. Cities most affected by the comet were blocked, guarded away, and quarantined, its remaining inhabitants left to die, while healthier cities became the safe havens for the healthy survivors. This event became known as the Contagion.

A mutated survivor from Manhattan, Walt Warland, while scavenging for food, water, and other necessities, comes across a passageway in the abandoned subway tunnels, suddenly finding himself in Equestria, a bright world of green grass, thriving crops, and blue skies inhabited by peaceful, talking ponies.

When its ruler, Princess Celestia, learns of Walt's plight on Earth, she sends him and six of her most trusted ponies on a quest to retrieve an artifact known as the Torch of Hopefyre, whose magic can eradicate the plague on Walt's planet and save mankind.

However, a violent and power-hungry gang of mutated scavengers, led by the equally violent and deadly Dada, comes across the passageway, Equestria, as well as learn about the Torch of Hopefyre. Now, not only will Walt and his new friends have to keep the Torch of Hopefyre's powers from Dada's grasp, but they must also save Equestria before his violent hunt for immense power dooms it as well.
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Inspired by many things:

Cloud Atlas (Sloosha's Crossin' an' Ev'rythin' After)
Dredd
James Bond films and books
Attack on Titan
Lots of fighting films