Weeks following her humiliating defeat in Ponyville, Trixie signs a contract with Discord to ruin Twilight Sparkle's life, unknowingly bringing about the end of Equestria in the process. With Twilight out of the way, Queen Chrysalis is never stopped, King Sombra is allowed to return, and the world is left in ruin. Now as part of her contract, Trixie is forced to save what little remains, as impossible as that may seem.
But that's all right. Discord's always there for her. Should she perish along her quest, he'll happily give her a sixty second restart to try again.
And again. And again. And again. And again. Until she gets it right, that is.