Vishnu Durga, also known as Narayani, is one among the numerous forms of Goddess Durga. Vishnu-Durga is regarded as the sister of Lord Krishna, born immediately before him. She is also known as Yoga Maya and is the child that flew away from the hand of Kamsa and warned him that
Krishna has already born on the earth and will annihilate him in near future.
Vishnu Durga shares many characteristics of Lord Vishnu including the dark complexion. She is four-armed and carries conch and discus (Sudarshana chakra) in her upper hand. Her normal right hand is in ‘abhaya posture’ – blessing or protection. Left hand is placed on her thigh
She is always depicted in peaceful form (Samumya Vadana). Sometimes she is depicted as standing on the head of the buffalo (Mahisha) killed by Durga.
(Source: Notes from Durga Kosha by Kalpatharu Research Academy)