Papa Purusha is an archetypal visualisation made use of in the practice of Tattwa Shuddhi, or the Inner Purification of the Elements. The practice evolved from writings in the Srimad Devi Bhagavatam and the Mahanirvana Tantra. This practice is essentially a detailed dynamic visualisation/meditation performed ritually, whereby one merges and dissolves geometric symbols (yantras) of the elements of the body into one another. It moves from gross to ever more subtle levels of energy vibration, and culminates in the divine form of Prana Shakti.
For anyone interested there is a Summary of Tattwa Shuddhi here ~ http://www.yogamag.net/archives/1983/joct83/bhuta1.shtml
This is not what this post is concerned about however. Papa Purusha is part of the visualisation employed in this technique, and he is interesting. He is a small, dark, male, about the size of the thumb, visualised in the lower left abdomen, and he is the ‘sinful man’, some might call Satan or the Devil. He is representative of the imbalance within us, psychological, physiological, spiritual. Eventually in the practice, this archetype is purified and transformed into a glowing egg that expands and fills the whole form.
Georg Feuerstein describes Tattwa Shuddhi and Papa Purusha quite efficiently…
This esoteric process is the basis for the bhuta-shuddhi ritual in which the elements are visualized as being purified through their progressive absorption into the divine Shakti. This practice is done prior to visualizing oneself as one’s chosen deity (ishta-devata) and doing ritual worship. The earth element governs the area between the feet and the thighs; the water element has authority over the area between the thighs and the navel; the fire element rules the zone between the navel and the heart; the air element is reigns over the section between the heart and the forehead; the ether element governs the area above the forehead. The practitioner visualizes earth dissolving into water, water into fire, fire into air, air into ether, and then ether into the higher principles (tattva) until everything is dissolved into the Goddess power itself.
Thus the yogin starts out as an impure being (papa-purusha) and through the power of visualization recreates himself as a pure being, a worthy vessel for the divine Power.
Another description of Papa Purusha here, from John Woodroofe…
“In imagination, the “man of sin” (Papapurusha) is burnt in mental fire, kundalini absorbs the centers, unites with Shiva, and then, redescending, recreates the centers, bathing them in nectar. By the mental representation of this process, the mind and body are purified, and the former is made to realize the unity of man and the Supreme Power, whose limited form he is, and the manner whereby the Universe is involved into and evolved from Shiva-Shakti. All these, and other rituals keep the mind of the Sadhaka occupied with the thought of the Supreme Power and of his essential unity with It, with the result that he becomes more and more that which he thinks upon. His Bhava, or disposition, becomes purified and divinized so far as that can be in the world. At length practice makes perfect in Sadhana, and on the arising in such purified and illuminated mind, of knowledge and detachment from the world, there is competency for Yoga. When in turn practice in Yoga makes perfect all limitations on experience are shed, and Nirvana is attained.”
– Shakti and Shâkta (ch 23 The Psychology of Hindu Religious Ritual) by Arthur Avalon (Sir John Woodroffe), 
Papa Purusha is the visualised as the embodiment of ”sin”.
” Visualise a little man the size of your thumb (in the left side of the abdomen). His skin is black as coal; he has fiery eyes and a large belly. In one hand he holds and axe, in the other a shield. His whole form is grotesque.”
~(Satyananda ~ Tattwa Shuddi )
The axe and the shield represent our habitual tendencies towards attack and retreat.
He ‘‘symbolises the cause of your pain and suffering on account of your ego, attachment, jealousy, pride, etc. ” (Satyananda).
Papa Purusha aught not be limited to some moral or ethical understanding, however, for he represents any and all of the natural imbalances between the vital forces within us. And these may be subtle energy forces such as between the lunar and the solar (ida/pingala, introvert/extrovert, active/passive, depressive/manic etc etc), any imbalance between mental and body energy, the natural conflicts that arise within our forms.
”Tantra emphasizes the necessity of experiencing conflict in order to attain harmony…..Without day there can be no knowledge of night….If there was no tension or conflict we would cease to evolve….Due to the strain (of conflict) we turn to spiritual experience and our evolution is pushed higher and higher.” (Satyananda)
”It is only when you face yourself objectively that you see many facets of your personality which your ego had previously concealed from you…which you are ashamed to confess you had…Tantra says You must be able to see yourself as you really are…to face your weaknesses as well as your strengths….a deep penetrating glare into yourself. Then you yourself will know what to do…” (Satyananda)
In the practice, the breath is used to transform the little man, to reduce him then through fire to ashes, to roll the ashes into a ball with the nectar from the moon, and then for this ball to be transformed into a radiant golden egg, which fills the entire body. Thus we have taken our knowledge of our darkest parts and transmuted it to light.
The Sadhaka having dissolved all in Brahman, a process which instills into his mind the unity of all, then thinks of the “black man of sin” in his body. The body is then purified. By breathing and Mantra it is first dried and then burnt with all its sinful inclinations. It is then mentally bathed with the nectar of the water-mantra from head to feet. The Sadhaka then thinks that in lieu of his old sinful body a new Deva body has come into being. He who with faith and sincerity believes that he is regenerated is in fact so. To each who truly believes that his body is a Deva body it becomes a Deva body. The Deva body thus brought into being is strengthened by the Earth-mantra and divine gaze. Saying, the Mantra “He I am” (So’ham) the Sadhaka infuses his body with the life of the Devi, the Mother of all.
I made a female form of Papa Purusha once, as it seems a little unfair, in my opinion, to consign all the bad stuff to the male archetype in this case.