Maha Navami or the ninth day of Durga Navratri is very important usually as it is the last day of Navratri. Mahishasura Mardhini is the fiercest form of the Goddess, who in which form she demolished Mahishasura. In 2010, Goddess Durga is decorated and worshipped as Mahishasura Mardhini on October 16th in most of the South Indian temples, especially in Vijayawada Kanaka Durga temple.
In Durga Saptashati, it is mentioned that Goddess Mahalakshmi with 18 arms (Astadasha bhujas) with all Devi& Devata Shaktis demolished Chamara and many demons and then Mahishasura. As the Goddess killed Mahisha on Navami day, it is known as Maharnavami.