This is one of the richest Hindu myths. It is a creation myth and also a trickster myth, and it is nested in the Vishnu myth cycle as an avatara (incarnation) myth. It has versions that are pan-Indian and versions that are sectarian (those used to prove the supremacy and ultimacy of Vishnu). When it functions as an origin myth, answering the question of how the gods (devas) became immortal, this myth also becomes a trickster myth—how the devas trick the demons (asuras) out of their share of the sacrifices and especially out of receiving the drink of immortality (amrita or amritsa). There are many versions of this myth, as well as many uses of it in other myths, both in the form of references to it and in the form of reversals of its themes.
In the sixth manvantara (world cycle) of the current kalpa (eon), the devas were losing in their battles with the asuras. One account said that the god Indra had slighted a brahmin sage named Durvasa and from that day on the power of the gods declined. So the devas went to Brahma, who immediately—as was usually the case in the Vaishnava myth cycle—counseled them to go to Vishnu.
Vishnu told the gods to follow his instructions exactly. They would have to work with the demons, but in the end Vishnu would enhance their glory. So the devas convinced the asuras that they must work together in order to obtain the drink of immortality. They would need to churn it up from the Milky Ocean (kshira-sagara). First herbs were thrown in the clear waters. Mount Manthara was used as a churning staff, and the giant snake Vasuki became the churning rope. The devas took Vasuki’s tail, while the asuras grabbed his head with its fiery breath. Vishnu became the support for the mountain as the turtle avatara (Kurma) and simultaneously took an invisible form and pressed down on the mountain from above. The gods and demons pulled back and forth with Vasuki, stirring the ocean and bringing all manner of things into being: Kamadhenu (the wish-granting cow), Varunidevi, Parijatam, the apsaras, Chandra-Soma (the moon), venom (halahala), which was absorbed by the serpents (nagas), Dhan- vantari with the pot of amrita, and Mahalakshmi. The avatara Kurma raised Mount Mandara when it started to sink. The demons grabbed the pot of amrita from the sage Dhanvantari and would have become immortal had they drunk it. But the demons were tricked out of their share when Vishnu appeared as Mohini and mesmerized them with her feminine charm and beauty. She told the asuras that she was lonely and looking for a mate. Mohini said that they should close their eyes and the one who opened them last would be the one she would marry. But Mohini went immediately to Devaloka (heaven) and gave the amrita to the devas. And even though the asuras attacked, the devas were strengthened by the divine drink and won dominion over the three worlds.