The ninth form of Ma Durga is the Ma Siddhidaatri. Ma Siddhidatri is the giver of all forms of achievements [Siddhi], which according to the Markand Purana are Anima, Mahima, Garima, Ladhima, Prapti, Prakaamya, Ishitva and Vashitva. As per the Brahmavaivart Purana there are 18 types of achievements which are Anima, Mahima, Garima, Ladhima, Prapti, Prakaamya, Ishitva,Vashitva, Sarvakaamaal, Saadhita, Sarvagynatva, DurShravana, Parkaayapraveshan, VakaSiddhi, Kalpavrushatva, Shrishti, Samharkaransaamarthya, Amaratva, Sarvanyayakatva, Bhavana and Siddhi.
Worshiping Ma Siddhidatri on the ninth day of navaratri one can obtain all this achievements [Siddhi]. As per Devi Purana, Bhagavan Shiva had attained all the achievements only by the grace of Ma Siddhidaatri. That is why his half body was that of the Devi and he was renowned as Ardhanareshwar. Dev-Danav-Gandharva-Kinnar-Yaksh-Manushya, all do worship Ma Siddhidaatri and attain achievements.
On the ninth day Pujan, Archan, Havan, etc of Mataji are performed. Ma Siddhidaatri can be pleased by chanting the above stated Mantra as many time. Te Conchshell, Chakra, Mace and lotus in the four hands of Ma Siddhidaatri signifies that she is always anxious to help us.