Anjalikastra is a celestial weapon in Hindu mythology. Anjalikastra was a personal astra of King of Gods- Indra. According to Hindu puranas/ithihasas, using this weapon on opponent, this cuts the head of the opponent. In some stories, it is also said that Lakshmana- brother of Lord Rama used same Anjalikastra to kill Indrajit. This astra came into prominence when Mahabharat's hero Arjuna used it to kill Karna.
In some versions of Ramayana, it is said that Meghanada was killed by the usage of Anjalikastra. Meghanada was granted a boon from Brahma that after the completion of the Yagna of his native goddess Prathyangira -"Nikumbhila yagna", he will get a celestial chariot, mounting on which, he will win over any enemy in war and become invulnerable. But Brahma also cautioned him that whosoever would destroy this yagna would also kill him. Indrajit through severe penance convinced Brahma to give him a boon in which it was promised to him that Indrajit would only be killed by such a man who hadn't had sleep for twelve years continuously. Thus Lakshmana was only the person at that time whose life satisfied those conditions and thus he was the only person eligible to kill Indrajit. Knowing this Vibhishana requested Lakshmana to destroy Indrajit's yagna. Lakshmana was very successful in spoiling Indrajit's Nikumbhila Yagna and finally killed Meghanada using Anjalikastra.
Mahabharat
On the 17th day of Kurukshetra war, Karna and Arjuna faced each other and started fighting. As the battle intensified, Arjuna pushed back Karna's chariot 10 steps backward every time by the energy of the arrows, but Karna failed to push Arjuna's chariot back. When questioned by Arjuna, Krishna said it is meant to be impossible for any human ever to push his chariot backwards because the chariot of Arjuna contains both Hanuman and Krishna, thus holding the entire weight of the universe. Being pushed back by Arjuna, Karna began coming forward but then Karna's chariot wheel was trapped in the mud as a result of the curse he had received earlier from goddess Earth. At the crucial moment, he forgot the incantations to invoke Brahmastra, as a result of his guru Parashurama's curse. Karna got down from his chariot to free the wheel and asked Arjuna to pause, reminding him of the etiquette of war. But Krishna spurred Arjuna to attack Karna reminding the way Karna killed Abhimanyu by stabbing him from behind- which are against the rules of engagement of the war. Being spurred by Krishna, then Arjuna used Anjalikastra to kill Karna which cut the head of Karna, leading to his death. In this way this astra was helpful for Arjuna in assassinating Karna and establishing Dharma on the Earth.
