Once upon a time there was a demon, he was also a devout follower of Lord Shiva. He performed incredible penance to get a blessing from Shiva. Because of his repentance, Mahadev agreed for his request and ask him for his wish. He requested immortality, but Shiva disagreed stating that the Gods are not supposed to give immortality to Demons, and asked him to demand for something else. Demon reluctantly agreed to change the boon he desired. He asked that the one whose head is touched by him should burn and transform into ashes, hence the name Bhasmasura (Bhasm means Ash, Asura stands for Demon). Shiva granted him this favour without any further thought.
Bhasmasura was too glad, but he decides to test the recently gained power on Lord Shiva himself. As he tried to touch the head of Shiva, Lord gets alert and escaped his reach. But everywhere Shiva went, he was pursued by Bhasmasura. Finally, Shiva, realising his mistake asked Vishnu for his help.
On hearing Shiva’s concern, Lord Vishnu agreed to help him. Vishnu appeared as Mohini and showed up before the demon. Mohini was so beautiful & attractive that No God, Demon or Human could escape her charm. Bhasmasura was also attracted to her. Bhasmasura asked Mohini to marry him. She replied that she was a dancer, and would marry anyone who would dance like her. Bhasmasura was so blinded by her beauty, that he agreed to imitate her dance steps. Mohini started to dance and Bhasmasura repeated her move, though not as well. The Dancing continued for some time, as Bhasmasura matched Mohini’s move for move. While dancing, Mohini made a pose where her hand was set on top of her own head. As Bhasmasura imitated her, he touched his head and was immediately burned and turned to ashes.
And another day was saved by Lord Vishnu or shall we say beautiful Mohini.