A gift from Varuna
At the burning of the Khandava forest, the sea god Varuna gives Krishna the discus and the mace Kaumodaki, and gives Arjuna the bow Gandiva.


Kaumodaki is the mace (gada) of Vishnu, held in one of his four hands with the discus, conch and lotus. The Mahabharata says the sea god Varuna gave it to Krishna at the burning of the Khandava forest, and the Vishnu Purana reads it as the power of the intellect.
The texts tell different stories.
At the burning of the Khandava forest, the sea god Varuna gives Krishna the discus and the mace Kaumodaki, and gives Arjuna the bow Gandiva.
The Purana explains Vishnu's ornaments and weapons as the powers of the cosmos, and names the mace as buddhi, the intellect.