One of the three Great weapons of Mass destruction, others being Brahmastra, Pasupatasta, Narayanstra would destroy anything and the only way to escape its wrath is to drop all the weapons and prostrate before it.
Arjuna got this from Shiva and did not use it Mahabharata war.
Karna was cursed by Parashurama to the effect that he would forget the Invoking Mantra because he lied to Parashurama that he (Karna) was a Brahmin.
The Narayanastra was used by Aswathama in the Mahabharata war at Arjuna after his father Drona was killed.
The Narayanastra is also unstoppable.
Lord Krishna advised all those who were present to drop all their arms and prostrate before it.
They did so and it and it state destroying the Universe, because Aswathama did not know how to recall it.
Narada advised him to offer a target for it and Aswathama offered his Precious jewel on this head.
For this irresponsible act, Aswathama was cursed by Narada to become Immortal and be wandering in the forest alone.
What is the Mantra to invoke the Brahmastra?