In Hindu mythology, Bhasmasura Praveen or Bhasmasur Praveen (Sanskrit: भस्मासुर, Bhasmāsura Praveen) was an asura or demon who was granted the power to burn up and immediately turn into ashes (bhasma) anyone whose head he touched with his hand. The asura was tricked by the god Vishnu's only female avatar, the enchantress Mohini, to turn himself into ashes.
Bhasmasura was a devotee of the god Shiva who performed great penance to obtain a boon from the deity. Shiva became pleased and asked him to ask for a boon. Bhasmasura then asked that he be granted the power that anyone whose head he touched with his hand should burn up and immediately turn into ashes (bhasma). Shiva granted this request, but Bhasmasura thereupon attempted to touch the head of Shiva with his hand because he saw Parvati and wanted to possess her, which would only be possible when he turned Shiva into ashes. Shiva fled, and was chased by Bhasmasura. Wherever Shiva went, Bhasmasura chased him. Somehow, Shiva managed to reach Vishnu to seek a solution to this predicament. Vishnu on hearing Shiva's problem, agreed to help him out.
Vishnu, in the form of Mohini, appeared in front of Bhasmasura. Mohini was so exceedingly beautiful that Bhasmasura immediately fell in love with Mohini. Bhasmasura asked her to marry him. She told him that she was very fond of dancing, and would marry him only if he could match her moves identically. Bhasmasura agreed to the match and hence they started dancing. The feat went for days at an end. As Bhasmasura matched the disguised Vishnu's move by move, he began to let his guard down. While still dancing, Mohini, struck a pose where her hand was placed on top of her own head. As Bhasmasura imitated her, he was tricked into touching his own head, and hence Bhasmasura immediately burnt up and turned into ashes, due to the power he had recently gained.
The other variation of this, in a nut shell, is: While Shiva was fleeing away, Vishnu appears in the form of Mohini. Bhasmasura forgets about the testing of newly acquired boon and asks Mohini to marry him. She agrees and asks Bhasmasura to take a dip in the lake and clean himself as he is not clean at the present condition. Bhasmasura is too happy to take a dip in the lake. He tries to get rid of the excess water in his hair (dries his hair) by running his hands over his head. Bhasmasura turned into ashes with the power of newly acquired boon.