In order to kill demons Shumbha and Nishumbha, Goddess Parvati removed her outer skin and revealed a dark skin; this avatar is known as Maa Kalaratri.
Maa Kalratri is the most vicious form of Goddess Parvati, as she represents her fierce side.
She is also known as Goddess Shubhankari because of her auspicious power to ward away demons.
