Nightshade is the daughter of Chrysalis and Sombra. They abandoned her when she refused to hurt ponies. A pony by the name of Phoenix takes her in and watches over her. Now she lives a normal life, but that will soon change
Chaos is not the opposite of Harmony but apart of it. Both chaos and order together create a balance known as Harmony. Without one you cannot have have the other and without either there is nothing.