The story of Bhadrakali and demon Shankachood is found in the Devi Bhagavat (9/56). Demon Shankhachuda was creating havoc in the world and Goddess Bhadrakali engaged him in a battle.
It became known from the voice from heaven that Shankachood could not be killed so long as he had ‘Samantraka’ – a divine mirror.
Angered, Bhadrakali had desired to use Pashupatastra to kill him. Hearing that voice from heaven, she stopped and using her hunger swallowed more than hundred armies of the demons.
While she was going to swallow Shankhachuda, he protected himself by the divine weapon, through which he started to expand himself.
After fainting from the strokes of the arms of the Goddess, he regained consciousness and bowed to the Goddess, but did not accept his defeat.
Shankachood later succumbed to Bhadrakali. He stopped using weapons and only neutralized the attack of the Goddess. In rage the Goddess threw him in the sky. After falling from the sky, he arose and again offered salutation to Bhadrakali. This was a strange incident. After seeing this situation, mother Bhadrakali herself went to Shankara and described the battle and sequential occurrence of incidents. She also narrated the incident of that bodiless voice from heaven. Shiva himself went to fight against Shankhachuda.