The Brothers' Conquest
Shumbha and Nishumbha had performed great tapasya and won the boon that no male being could kill them. They drove the gods from their kingdoms, claiming all the treasures of the cosmos — including the divine elephant Airavata and the horse Ucchaishravas.
The gods in desperation praised the goddess and prayed for her help.
Parvati, bathing in the Himalayas, heard their prayer. From her body emerged a golden woman — Ambika (also called Kaushiki — the one who emerged from the sheath). The original dark form of Parvati became Kali in this moment of splitting.
The Pursuit
Ambika was the most beautiful form ever seen. When Shumbha's envoys saw her in the Himalayas, they rushed to tell him. He sent his greatest generals — first Dhumralochana, then Chanda and Munda.
Each was destroyed. Ambika killed Dhumralochana with a battle cry. She killed Chanda and Munda — and from that act was given the name Chamunda by Kali who witnessed it.
Then Raktabija came — described in the story of Kali's battle. He too was destroyed.
The Final Battle
Shumbha and Nishumbha came themselves. The battle was immense.
Nishumbha fell. Shumbha challenged Ambika directly: "You fight with the help of others. Fight me alone."
Ambika smiled: "I am alone. All those forms you saw — Kali, Chamunda, the others — were my own forms. I am one. All power in the universe is mine."
She destroyed Shumbha.