A thousand years after the Princesses disappeared from Equestria, Twilight Sparkle meets a lost Cloudsdale scout named Rainbow Dash. Together they look for a way to end the thousand-year night and dispel the darkness that has spread across Equestria.

Edited by Pascoite
Contains fairly mild grim-dark. Inspiration taken from the Dark Souls games, but it's not strictly a crossover.
Chapters titled "Arc #: Chapter Name" are part of the main story. Chapters titled "Character: Chapter Name" are one-shots about other characters, set in the same world, and aren't necessary in order to follow the main story.

Bioshock meets MLP in this psychological thriller, where Celestia's new faithful student, Siren Song, must discover the truth behind the city beneath the waves.

Beautiful, gifted, and faithful student of the Princess of the Sun, Siren Song has very nearly everything a pony could want. Sometimes though, in the twilight hours, Siren can see the sadness in her mentor's eyes. Once, ponies whisper, the Princess had another student named Twilight Sparkle, but she left Equestria, never to return. The pony who has a perfect life just needs one more thing—to convince Twilight Sparkle to come home so the Princess will smile again. But when Siren arrives in pursuit of Twilight, she soon finds herself trapped in a city of horrors, with only its monstrous denizens for help.

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This story is a sequel to Siren Song

Bioshock meets MLP in this psychological thriller, where Celestia's new faithful student, Siren Song, must discover the truth behind the city beneath the waves.

Since arriving in Vision, Siren has done things she never thought she was capable of—all in the name of survival. But now she abandons safety to gallop back into the darkness. Determined to do the right thing in a city gone mad, Siren must face the horrors she once fled from. But all is not as it seems in the vast and dark ocean, and Siren’s greatest foe may yet lie within herself.

Book 2 of the Vision series. Sequel to Book 1: Siren Song.

Now with a TV Tropes page!