Twilight never did find Cadance in the caves. Years have passed without books or company as a villain has her way with equestria. Her despair and past exploits have attracted The Outsider, who has long since grown bored with Corvo's world. Will his mark be enough for Twilight to overcome obstacles internal and external? The Outsider can't wait to find out.
(Dishonored Crossover, no humans in this one. The Outsider doesn't count.)