Mahavidya Mantra/महाविधा मन्त्र: The guardian of the universe Lord Vishnu’s internal power is called Mahavidya Mantra. This goddess is visibly or invisibly is the root of evolution of the universe. The evolution of Lord Brahma, Vishnu and Shiva occurred according to it. For the smooth operation Mahamaya(Mahavidya Mantra) empowered of the universe Lord Vishnu became guardian, Lord Brahma became the creator and Shiva became the destroyer.
In this way all the three gods became the symbol of entity, sage and darkness qualities/Mahavidya Mantra. According to these three gods, there were three goddesses, Mahakali, Mahalaxmi and Mahasaraswati. All the three were deputed with their work. Among them Mahalaxmi has the saatvik power of Lord Vishnu, Mahasaraswati has the regal power of Lord Brahma and Mahakali has the power of darkness of Lord Shiva.
During the period of evolution Lord Shiva explored the genesis of cracy (Tantra) along with the power of his better half Parvati, who actually was Mahakali with the power of darkness and take the fierce look and appearance. But her fierce appearance is meant only for the wrong things and people and Asuras/Mahavidya Mantra. Otherwise this goddess is benign, benign-vehement and vehement in three forms, and according to the nature it is divided in two parts, Sree Kul and Kali Kul.
This goddess according to work and qualities appeared in many reincarnations. It is not that she always appeared in fierce form(Mahavidya Mantra). When she appeared in benign form, she was cool and soft. In benign-vehement form she is in both type of nature and in vehement form she is terrible in nature. In this way she appears in ten forms called Yogini, Dakini etc. and all they have different nature and qualities.