Singhamukha is the "lion faced" dakini, a fierce tamer of curses. She is connected with Vajrayogini and Heruka, and can be found in the Tibetan Book of Living and Dying.
A dakini is a kind of "angel" or deity, a female embodiment of enlightened energy. Their purpose is to transform negative energy. A dakini can be a guru, yidam, or protector. Singhamukha is a wrathful dakini, and her lion face represents her great power.