Dissociative Identity disorder. Also known as multiple personality disorder. Rosemary was diagnosed with this condition when she was just a filly. She had discovered that hidden inside her was a whole other pony-a thieving, sly mare. And when that mare came out, all hell broke loose. Now Rosemary moves to Ponyville to start a new life-but as she learns the hard way, you can never fully escape your past.