In order for the Asuras to regain their powers they needed to form an alliance with the Devas, perform the samudra manthan, and drink the amrita nectar. This amrita nectar would return the lost powers of the Devas back to them. But there was a slight problem with this plan. If the Asuras were able to get a hold of this nectar then they would also regain their powers, leaving the Devas right back where they started. So, the Devas went to Vishnu for help.
Vishnu agreed to help the Devas perform the samudra manthan and prevent the Asuras from obtaining the amrita nectar. Mandara, a huge mountain, sat in the ocean as one of the axes of the world and was used as a rod to stir the waters. Vasuki, the giant snake that spent its time wrapped around Shiva's neck, offered to be used as the churning rope for the great task. After Vasuki had wrapped itself around the great mountain, the Asuras demanded to hold the head of the great snake, which the Devas allowed.
But the mountain would not stay afloat. Every time the Asuras and Devas tried to churn the waters the mountain would begin to sink. So Vishnu transformed himself into a mighty tortoise and rested the huge mountain on the top of his shell, keeping the mountain afloat.
Then, they began pulling back and forth on Vasuki and the mountain began to turn like a top on the shell of Vishnu. As the mountain began to turn, Vasuki started to emit poisonous fumes from his mouth, poisoning the Asuras on that side of the snake. But still they kept pulling and churning. Soon, the ocean began to release a great number of beautiful gifts and treasures.
Chandra, the moon was released from the frothing waves. Indra's elephant mount, Airavata, was released, and Kamadhenu the cow of plenty came leaping from the ocean like a rocket into the sky. Lakshmi, the future wife of Vishnu, emerged from the tidal waves, along with Vishnu's conch, Panchajanya, as well as his magical bow and mace.
But at last, Dhanvantari, the physician of the gods, rose from the depths, holding the one thing that both parties sought. This most precious gift that was released was the pot of amrita that was so strongly desired by both parties. Once it was released, the Asuras forcefully took it away, quite possibly jeopardizing the Devas' chances of ever regaining their powers again...
*Author's Note*
- I did not add very many changes to this part of the story. The original is so fascinating that I decided that (for now) I did not want to stray too far from the original. It is stories like this that make being a Religious Studies major worth it because there are not very many creation stories like this. So many key elements to Hindu lore, like Lakshmi and Airivata, emerge from this event. The only changes that I truly made were the order in which my source recounted Vishnu turning into the turtle and Vasuki wrapping around the mountain. Some sources had Vishnu supporting the mountain first, and then talking about Vaskui being used as the rope, some sources had it the other way around. I decided to stick with Vasuki being used as the rope, the Asuras and Devas realizing the mountain wouldn't stay afloat, and then Vishnu becoming the turtle. That sequence just made more sense to me. I also didn't see anything saying that Lakshmi emerged holding all of Vishnu's new toys, but since she was his future wife, I decided it not only read better to do it that way it also helped piece those emerging things to Vishnu.