Ages have been both written and forgotten by Atrus. His writing has brought him both great happiness, but also great suffering and struggle. Equestria was an Age that had been forgotten by Atrus more than a decade ago that he’d written as a gift for his daughter, Yeesha, when she was very young. Twilight, in her curiosity, found a book in the library of her new castle labeled “Tomahna” bringing her to Atrus’s home. Her arrival put her in the middle of a scheme that could separate her from Equestria forever.

(A Myst and MLP crossover)