Krtya is a demoness of ferocious form and is invoked by chants and mantras by sorcerer to get rid of enemies. In the story of Prahlada, the young devotee of Vishnu, Demon Krtya was invoked. The story is found in the Vishnu Purana.
As per Vishnu Purana, Prahlada was a child but he was one of the greatest devotees of Vishnu. All attempts by his teachers and his father, Hiranyakashipu, failed to deflect the young child from the path of devotion to Vishnu.
Finally, numerous attempts were made to kill Prahlada. But nothing worked.
Then the priests of Hiranyakashipu invoked the monstrous Krtya through chants.
She shot a fiery javelin at Prahlada.
But it could not destroy young Prahlada instead the javelin broke into pieces and was destroyed.
Thus repulsed, Krtya turned against the priests, destroyed them and disappeared.
With Demon Krtya, if the intended target is not found, she destroys the person who invoked her.