Despite having the knowledge of Mrit Sanjeevani Mantra (मृत संजीवनी मंत्र) - which could bring back anyone dead back to life again, Why didn't (or not able to maybe) Shukracharya revive Hiranyakasha, Hiranayakashipu, Meghnad or Raavan etc?
Can I get specific instances where he exactly used the Mrit Sanjeevani Mantra and was successful in reviving. Is there any kind of limitations on what kind of dead person is eligible to be revived. For example - burnt to ashes or decapitated or other forms of death? Or whether who killed the person also matter? For example - if the person was killed by Shiva or Shakti or Vishnu, can that be revived too? ( I watched in this show Vishnu Puran, where Shukracharya says that he cannot revive a particular demon because it was killed by Vishnu himself)