Magni's Knife is a weapon that belongs to the Aesir god, Magni. It was going to be introduced in God of War (2018), but was subsequently scrapped from his design, making Magni's Cyclonic Blade the only weapon we see him use in God of War (2018), and the God of War Ragnarök: Valhalla DLC.
In God of War Series[]
This knife was created for Thor's eldest son, Magni. It is never directly specified on how Magni acquired these weapons, although we can assume based on few sources the weapons were created by Asgardian smiths (Just like his sister's weapons). The knife is never seen being used in combat in God of War (2018), or the God of War Ragnarök: Valhalla DLC. This would be due to the fact it never made the final cut in Magni's overall design.