Pashupatastra (pāśupatāstra)

The Pashupata is Shiva's own weapon, discharged by mind, eye, word or bow, and said to be able to destroy creation itself. Arjuna wins it during the exile by austerity in the Himalayas and by wrestling a mountain hunter who turns out to be Shiva testing him, and is warned never to use it against a lesser enemy. He never does discharge it in the war, which is the Mahabharata's way of showing that restraint, not power, is what separates him from Ashvatthama.