Queen of Darkness

Violet is the prettiest girl in the whole state. She is also one of the nicest girl in the day. However, she has another side to her that is unknown to anyone in the universe. While in the day she is the nicest girl you would ever be able to think of, at night she becomes an evil creature. A monster in the dark. She glides through the air silently. She could zoom past through places in less than a second. Who is she and what does she want?