I imagine a story in alternate universe where Rarity was an investigator/sheriff of a medieval camp/village, and Applejack was her agent. Rarity made her swear by her skin that she'll always be telling the truth, but once Applejack received a lie because of a conspiracy, and then Rarity violently punished her. Bleeding, Applejack escaped into Everfree, where the witch Zecora and her gang of Untouchable healed her and she thought she didn't have her Honesty reputation anymore because she betrayed her tribe's code, and became the Black Avenger always wearing a black robe, attacking Rarity's camp until it was in fear, and so a legend appeared.