Queen Sombress

Queen Sombress is a long kept secret of the cristail empire. She was the evil behind King Sombra, the love of his life, and the motivation behind his determination to make the cristail empire vanished when he was first defeated. She was the first one who tried to actselly stop Celestia and Luna and prevent them from robbing her rule of the cristail ponies. She actselly even almost managed to defeated them, until Heaven's Light and Nightus came in the last minute, took over the fight, and defeated Sombress, imprisoning her in a cristail sarcofigus that is lost in the hidden corridors of the cristail empire, where it would stay even after Sombra's second defeat.... that is, until curious exploriors find it. And if during Sombra's allience in the villain leage, this could be trouble.

Appearence.
She resembles this.

(http://images2.wikia.nocookie.net/__cb20131107043657/mlp/images/0/02/FANMADE_Queen_Sombra.png)