I don't know if Octavia and Daring Do are bad, but I know for sure Trixie and Gilda are! If you do want to have a good character turn evil, my suggestion would be Octavia. I would do an evil Princess Twilight or Celestia who would go against some custom made or background ponies. Background ponies that are are not known as well as others. For instance, Lyra and Bon-Bon (and Derpy!) are known more than ponies like Roseluck, Cherry Spices, and Sweetie Swirl! Anyways, good idea to do a poll before you write the Fanfiction, Poetic Justice!