Maa Siddhidatri would be the ninth avatar of maa Durga and is particularly worshipped on the 9th day of navratri. Ma Siddhidatri is represented with four arms sitting on a beautiful lotus flower. When Mahishasura came to understand that the gods had sent a lady to get rid of him https://www.youtube.com/watch?v=S1HpMpEww4Q