1. Sudarshan Chakra 
The infallible discus of Lord Krishna. It is the embodied form of his supreme energy and considered to be the wheel of time which is above all the entities in the universe. The discus emerged as “Ayudha Purush” representing a fierce form of Lord Krishna for the purpose of destruction of the demons. The centre of Sudarshan Chakra is composed of Vajra the powerful thunderbolt which surrounds the six navels. There are twelve spokes in the discus which represent the twelve deities known as Adityas. The outer rim of the discus is adorned with one thousand spikes. Lord Krishna used Sudarshan Chakra to kill asuras like Shishupala, Dantavakra, Mura and Naraka.
2. Kaumodaki mace 
The invincible mace of Lord Krishna. The word “Kaumodaki” is derived from the word “Kumunda” meaning water lily. The head of the mace looks like a full-bloomed water lily. Kaumodaki mace represents power and intellect. Lord Krishna used the mace to fight with the two invincible demons Madhu and Kaitabha.
3. Narayanastra 
The personified weapon of Lord Krishna in his four-armed Narayana form. In the Mahabharata era, the knowledge of Narayanastra was known to Drona and his son Ashwatthama. When fired, the weapon manifests as a circular projectile in the sky. The weapon roatates in the sky and showers down upon the enemy innumerable arrows, swords, maces, lances, spikes, darts, javelins and bludgeons. Ashwatthama invoked Narayanastra upon Pandava army on the 15th day and killed millions of Pandava soilders.
4. Vaishnavastra 
Lord Krishna has four forms. His first form is always engaged in austerities for the welfare of the world. His second form beholds the virtuous and evil deeds in the universe. His third form takes incarnations for the establishment of law and order. His fourth form lies down in the ocean of milk and sleeps for thousands of years. This final form wakes up at the end of every one thousand years and grants the best of boons to the devotees. Once Goddess Bhumidevi approached Lord Krishna in the ocean of milk when he arose from his deep slumber after one thousand years. Bhumidevi asked for the boon of a lethal weapon known as Vaishnavastra. Lord Krishna granted the wish and gave her the boon of the weapon. Later Bhumidevi conferred the boon of Vaishnavastra to her son Naraka. The saga of the weapon continued as Naraka bestowed Vaishnavastra to his son Bhagadatta. In Kurukshetra war, Bhagadatta hurled the weapon to kill Arjuna. However Lord Krishna who was Arjuna’s charioteer stood ahead of Vaishnavastra and consumed the weapon. Upon reaching Lord Krishna’s neck, Vaishnavastra turned into a garland of flowers.
5. Nandaka sword 
The sword of Lord Krishna. Once Brahma was performing a sacrifice on the bank of the river Ganga. When he sat in deep meditation, a demon named Lohasura approached there with the intention of disrupting the sacrifice. During that time a deity emerged out of Brahma who turned into an excellent sword. At the same time, Lord Krishna appeared out of nowhere to prevent the disruption of the sacrifice. Wielding the sword on his hand, Lord Krishna cut Lohasura into pieces each of which became a metal. Lord Krishna took the sword and eventually departed for his abode.
Image(s) courtesy: Google