In places in the tantrik tradition, the Krishna avatar of Vishnu is often identified with Kali. This reaches a peak in the Tantrarajatantra, where it is said that having already charmed the world of men as herself, Lalita took a male form as Krishna and then proceeded to enchant women. In this work, Krishna has six forms, identified with the six senses (including Mind). They are Kamaraja Gopala, Manmatha Gopala, Kandarpa Gopala, Makaraketana Gopala and Manobhava Gopala. Their meditation images (dhyana according to the same work, describes them as being like dawn,with six arms, holding flute, noose, goad, sugar cane bow and a bowl of curds. These are the five arrows of Lalita and the bow and here Krishna is identified with Kameshvara, the Indian god of love, who is otherwise called Ananga, and, like Cupid, is armed with a bow.
The Kalivilasa Tantra, a Bengali work, states Krishna was born as the son of Devi who was golden (Gauri) and turned black when he was excited by passion. In the Todala Tantra, each of the ten Mahavidyas, forms of the supreme Goddess, has her own male counterpart and here Krishna is said to be the spouse of Kali. There are many images of Krishna in India which show him as black. An Indian commentator to the hymn to Kali called Karpuradistotra, goes further and says that there is a connection between the bija mantra of Kali which is Krim, Krishna and Christ. Whatever the truth of that identification, it is certain that to many ordinary folk in India, Krishna and Christ do have a resonance. Often you will see contemporary images of Krishna and Christ together in the inside of houses. Krishna (and his tantrika counterpart Kameshvara) are moved by love (prem).
The Victorian print at the top left of this page shows Radha, Krishna's shakti, worshipping Krishna as Kali, while the image on the left is a contemporary print (copyright acknowledged but of unknown provenance).
In the Brihat Tantra Sara, a large compilation of tantrik rites, Krishna appears as a fully-flowered tantrika devata, with his own yantra, gayatri, mantra and puja or ritual which uses this yantra (click on this image for full size yantra). In the hexagon in the centre of the yantra, the following words appear: Krishnaya Govindaya Klim sadhya Gopijanavallabhaya Svaha. In the corners of the hexagon are the bija mantras Hrim and Shrim. Outside the hexagon is the Krisna mantra which runs: Klim Krishnaya Namah. In the petals of the yantra is a longer mantra Namah Kamadevaya Sarvajanapriyaya Sarvajansammohanaya Jvala Prajvala Sarvajanasya Hridayamavamsham Kurukura Svaha. Around the eight petals are the Matrikas or letters of the Sanskrit alphabet while in the angles of the protecting wall are bija mantras Hrim and Shrim, once more.
Although commonly associated with Shaivite and Shakta concerns, in reality there is no sectarianism in the tradition. In many of the texts of the tradition, it is stated that it is only a fool who makes any distinction between the two. The forms of Vishnu, however, often have a more emotional tinge to them than those of Shiva, who can be portrayed as a highly terrifying figure. Trailokyamohana Vishnu, for example, in thePrapanchasara Tantra, is meditated upon as in the middle of a garden of Aeon Trees, scented with flowers and musical from the sound of bees, with his shakti Shri Lakshmi. She is bathed in sweat from her passion for him while around them both are the women of the household, all pierced by the arrows of Kama, god of sexuality, all shameless with their passion.Copied from http://www.shivashakti.com/krishna.htm