Changes

* According to Padma purana (Bhumi Kaanda, Chap 23), Hiranyakasipu, the son of Kashyapa Prajapati and his wife Danu, is killed by Mahavishnu for his wrong asuric deeds. Kashyapa grants her another powerful son Vala or Bala, whom Indra kills with his Vajraayudha for stealing the cows. Angered Kashyapa plucked a hair and made a burnt offering of it, saying that a son would be born who will be the destroyer of Indra.       

* According to Padma purana (Bhumi Kaanda, Chap 23), Hiranyakasipu, the son of Kashyapa Prajapati and his wife Danu, is killed by Mahavishnu for his wrong asuric deeds. Kashyapa grants her another powerful son Vala or Bala, whom Indra kills with his Vajraayudha for stealing the cows. Angered Kashyapa plucked a hair and made a burnt offering of it, saying that a son would be born who will be the destroyer of Indra.       

* According to Devi Bhagavata (Skanda 6)  त्वष्टा॥ Tvastha angered by Indra's killing of his son विश्वरूप || Vishwaroopa (also called Trisiras), initiates an आभिचारिकं यागं || aabhaicharikam yagam (a yagam performed to cause harm to an intended person) to procure a son to kill Indra.  

* According to Devi Bhagavata (Skanda 6)  त्वष्ट्रा ॥ Tvasthra angered by Indra's killing of his son विश्वरूप || Vishwaroopa (also called Trisiras), initiates an आभिचारिकं यागं || aabhaicharikam yagam (a yagam performed to cause harm to an intended person) to procure a son to kill Indra.  

The ऋत्विज || ritvijas were to utter the mantra "इन्द्रशत्रुर्वर्धस्व" with अन्त उदात्तः ॥ Anta Udaatta or Udaatta swara in the end of the mantra (to mean Prosper Oh ! Enemy of Indra) instead they used the आद्य उदात्तः ॥ Aadya Udaatta swara in the beginning of the mantra (meaning Oh! Indra, one who has enemies, Prosper). The meaning of the mantra changed with the improper utterance of the swara. So instead of asking for the rise and prosperity of a son to take revenge on Indra, the ऋत्विज || ritvijas asked for the prosperity and glory of Indra who destroyed असुर || Asuras. Thus वृत्रासुर '''||''' Vrttrasura the son of त्वष्टा ॥ Tvastha was born, an enemy of Indra, but eventually Indra was rewarded with glory in killing वृत्रासुर '''||''' Vrttrasura. 

The ऋत्विज || ritvijas were to utter the mantra "इन्द्रशत्रुर्वर्धस्व" with अन्त उदात्तः ॥ Anta Udaatta or Udaatta swara in the end of the mantra (to mean Prosper Oh ! Enemy of Indra) instead they used the आद्य उदात्तः ॥ Aadya Udaatta swara in the beginning of the mantra (meaning Oh! Indra, one who has enemies, Prosper). The meaning of the mantra changed with the improper utterance of the swara. So instead of asking for the rise and prosperity of a son to take revenge on Indra, the ऋत्विज || ritvijas asked for the prosperity and glory of Indra who destroyed असुर || Asuras. Thus वृत्रासुर '''||''' Vrttrasura the son of त्वष्टा ॥ Tvastha was born, an enemy of Indra, but eventually Indra was rewarded with glory in killing वृत्रासुर '''||''' Vrttrasura.