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The Pashupatastra ( IAST: Pāśupatāstra, sanskrit: पाशुपतास्त्र), in Hindu History, is an irresistible and most destructive personal weapon of Shiva, Kali and Adi Para Sakthi discharged by the mind, the eyes, words, or a bow. Never to be used against lesser enemies or by lesser warriors, the Pashupatastra is capable of destroying creation and vanquishing all beings. Pashupatastra is the most destructive, powerful, irresistible weapon of all the weapons mentioned in the Hindu mythology. The only weapon that can neutralize Pashupatastra is the Kameswaraastra which is the personal weapon of Lord Kameswara, the consort of Adi Para Sakthi.
In the Mahabharata war Arjuna obtained this weapon from Lord Shiva. Apart from Arjuna, Indrajit the son of Ravana also possessed Pashupatastra as per the Hindu epics. It is also said in Ramayana that when Indrajit used Pasupathastra against Lakshmana it doesn't harm him because Lakshmana was the part incarnate of Lord Vishnu and Sesha.
A Narrative from Kisari Mohan Ganguli translation of Mahabharat regarding the power of Pashupatastra:
O thou of mighty arms, that weapon (Pashupatastra) is superior to the Brahma, the Narayana, the Indra, the Agneya, and the Varuna weapons. Verily, it is capable of neutralizing every other weapon in the universe. It was with that weapon that the illustrious Mahadeva had in days of yore, burnt and consumed in a moment the triple city of the Asuras. With the greatest ease, Mahadeva, using that single arrow, achieved that feat. That weapon, shot by Mahadeva's arms, can, without doubt consume in half the time taken up by a twinkling of the eyes the entire universe with all its mobile and immobile creatures. In the universe there is no being including even the deities, that are incapable of being slain by that weapon.