My alicorn OC Princess Yin. I made her a couple of years ago and decided to update her look. In my headcanon, Yin and her husband King Yang were the Royalties of Harmony. They both ruled and mentored the two sisters before Yin was possessed by the Tantabus, an ancient evil spirit that control the will of ponies who let it.  
Yin is kinda introverted and she struggles to trust anyone. She, along with StarSwirl, help Celestia with her magic studies. Yin is kind though and wants the best for her subjects, she is said to be one of the most beautiful ponies in her time.