Maa Katyayani is worshipped on the sixth day of Navratri.

Devotees of Maa Durga worship Maa Katyayani, who killed the demon king Mahishasura, on this day.
According to Hindu mythology, Lord Brahma, Vishnu, and Shiva combined their energies to create Maa Katyayani. They manifested this anger in the form of energy rays which crystallized in the hermitage of Katyayana Rishi, who then gave it proper form. This is why this form of Maa Durga is also known as Katyayani or the daughter of Katyayana.
She is regarded as one of the most violent forms of Goddess Durga. The Goddess killed the demon king Mahishasura, which is why she is known as Mahishasurmardini. She rides a lion and is depicted with four hands that carry a lotus flower and sword on the left side and Abhaya and Varada Mudras on the right. Maa Katyayani is considered the destroyer of evil.
Maa Katyayani governs the planet Brihaspati. She symbolizes intelligence and peace. It is said that the blessings of Goddess Katyayani can wash away the sins of the worshippers, remove negative forces, and clear hurdles. Additionally, on the day Maa Katyayani is worshipped during Navratri, unmarried girls keep a fast to get a husband of their choice.
The colour of the day on the sixth day of Navratri is grey. It represents balanced emotions and keeps the person down-to-earth. Devotees can wear this colour on this day to achieve all these qualities.

In Shaktism, she is associated with the fierce forms of Shakti or Durga, a warrior goddess, which also includes Bhadrakali and Chandika.
Her exploits are described in the Devi-Bhagavata Purana and Devi Mahatmyam, part of the Markandeya Purana attributed to sage Markandeya Rishi, who wrote it in Sanskrit ca. 400-500 CE. Over a period of time, her presence was also felt in Buddhist and Jain texts and several Tantric texts, especially the Kalika-Purana.
In Hindu traditions like Yoga and Tantra, she is ascribed to the sixth Ajna Chakra or the Third eye chakra and her blessings are invoked by concentrating on this point.
6th day of Navratri : Katyayani Mata Mantra
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