Note: I'll accept any story with an O.C., just so long as they get their Cutie Mark or explain how they got it at some point of the story. Past Sins by Pen Stroke, for example, has Nyx getting her Cutie Mark at one point, even though that isn't entirely the main point of the story, while Fallout Equestria by KKat, for example, has a scene where Calamity talks about how he got his (former) cutie mark.