Fire God in one of the adhyayas of Agni Purana has enumerated the various sorts of Mantras and has described the processes of performing their respective rites of Shodanyasa, which admits of threefold division. In the chapter related to the rite of Shodanyasa three different types of Shodanyasa have been explicitly described. The three classes are as follows Shakta, Shambhava and the Jamala class.
The Purana says that the Shambhava class of Shodanyasa is characterised by six terms tied together with sixteen knots. The Nyasa in this rite enjoins the contemplation of the three sorts of knowable (Trividya) and connotes the full realisation of the three fundamental principles within the inner self of the votary. The Nyasa
appertaining to the fourth form of worship consists of twelve Shlokas or letters, while its fifth and sixth forms are respectively marked by features known as the Ratnapanchatma and Navatma in the phraseology of the Tantras. It is said that in the case of a Shakta or a worshipper of the goddess of energy (Shakti), the rite of Nyasa touches the principle, known as the Trividya, while in the second or the Shambhava form of worship the eight different attributes of the Lord Shiva
known as the Aghoryastaka should be psychically located. In the Shambhava form obeisance should be offered to various parts of the body, the goddess of illusion and to many other aspects of life.
The Mantras to be used in connection with a Shodanyasa in a Shakta form of worship, consists of the letters from "Na to Fa". Nadini should end with the letter "sha". The Nyasa is to be performed as follows:-"may the letter `Da` which is the emblem of peace be located in the head, and may the goddess Chamunda
preside over the three eyes, may `Dha` which smoothes the eyes, occupy the two external organs of the sight and may the goddess Gujhya Shaktini (goddess of occult energy) take her seat within the nostrils. May the letter `Na` which is the symbol of the goddess Narayani, fill the cavities of the ears with her peculiar celestial essence, and may the goddess Tamohani (the gloom-dispelling goddess) take her abode inside the right ear. May the letter `ja` which is the symbol of wisdom occupy the left ear, and may the thunder-wielding goddess (Vajrini) take her seat in the mouth. May the letter `Ka` which stands for the goddess Karalli (the goddess Karali (the goddess of horrible features) be located in the right tooth, and may the letter `Kha` which is emblematic of the goddess Kapalini (goddess bedecked with human skulls) take her seat on the left shoulder, may the letter `Ga` shield the upper tooth with the divine essence of Shiva whom it represents, and likewise may the goddess Ghora together with the letter `Gha` which is the phonetic symbol of her peculiar celestial prowess, take her seat on the left tooth.
May the vowel letter `U` as well as the goddess Shikha occupy the rows of the teeth, and may the resplendent image of the vowel letter `E` which is emblematic of the principle of illusion be located in, and may the resplendent image of the vowel letter `E` which is emblematic of the principle of illusion be located in, and cover with, its proper and representative virtue of the sense organ of taste. May the goddess nageshavari, whose attributes stand symbolised in the (fiery) character of `a" be located in the speech, and let him locate by means of the soul-light the letter `V` in the throat which is the phonetic symbol of the divine attributes embodied by the peacock riding goddess. May the letter `Bha` which is exponent of the divine attributes of the terror-inspiring goddess(Bhisani) be similarly projected into the region of the right shoulder, and let him contemplate the letter `Ma` clad in the effulgence of its presiding deity (Vayubega or the goddess swift as the wind) as psychically projected into the region of the left shoulder. Similarly let the votary contemplate the right arm as permeated with the psychic principle represented by the letter `Da,` and may the left arm be similarly strengthened with the virtue of the divine attributes of the god Vinayaka (the grantor of success in all sorts of undertakings) and which are symbolised by the consonant letter `Dha.` May the two hands be stuffed with the essence of the night of the full moon as represented by the letter `Pa,` and may the fingers be permeated with the effulgence of the vowel letter.
The worshipper during the right of Shodanyasa has asked the lord that to grant him with an imagination power with the help of which he would imagine the fingers of his left hand as filled in with the illuminating principle represented by the conjunct `Ang,` and may the conjunct `As,` which is emblematic of the vitalising principle of the universe, permeate the palm of his hand.
Similarly the votary should psychically project into the region of his forehead the letter "Dha" which represents the principle embodied by the goddess (kapalini) wearing a garland of human skulls, while the letter "Ta" with its illuminating principle should be located in the region of the Shuladanda by an act of mental abstraction. The letter "Ja" which is the symbol of the attributes of the goddess Sadhini should be contemplated as presiding over the process of growth. The letter "Sha" which is representative of the supreme goddess should be deemed as located in his soul, while he should contemplate his vital principle as permeated with the esoteric significance of the letter "Ha" which is the exponent of the divine essence of the goddess Ambika. The letter "Chehha" which is the symbol of the goddess Sharira should be contemplated as permeating the region of the right breast, while the letter "Na" which stands for the monsters Putana
, should be contemplated as located in the region of the left breast. The vowel letter "A" should be contemplated as permeating the milk, while the vowel letter "A" which is emblematic of the attributes of the goddess Lamvodari, should be located in the belly. The conjunct "Ksha" which is emblematic of the goddess of death (Sanharika), should be located about the region of the umbilicus.
While discussing the rite of Shodanyasa Lord Agni
states that the region of the heart should be contemplated as burning with the effulgence of the letter "Ma" which symbolises the attributes of the god Mahakala, while the letter "Ya" which is emblematic of the attribute of the god of speech should be contemplated as located in the faculty of memory.
Finally the adhyaya on Shodanyasa ends saying that a votary having performed the Nyasa and by worshipping the attributes of the god Rudra with the Hreeng Mantra may hope to attain every thing worth having in this world.