In the Poetic Edda poem Völuspá, the Æsir-Vanir War is described as officially starting when Odin throws a spear over the heads of an assembly of Vanir gods. Whether or not this was specifically Gungnir is, however, unstated. In Sigrdrífumál, the valkyrie Sigrdrífa advises Sigurd on the magical application of Runes. She gives Sigurd advice and shares with him lore, including that runes were carved on the tip of Gungnir.
According to chapter 51 of the Prose Edda book Gylfaginning, Odin will ride in front of the Einherjar while advancing on to the battle field at Ragnarök wearing a gold helmet, an impressive cloak of mail and carrying Gungnir. He will then attack the wolf Fenrir with it.
In Skáldskaparmál, more information regarding the spear is presented. the spear was fashioned by the dwarfs known as the Sons of Ivaldi under the mastery of the blacksmith dwarf Dvalin. The spear was obtained from the dwarfs by Loki, the results of a scheme he concocted as a partial reparation for his cutting of the goddess Sif's hair. The spear is described as being so well balanced that it could strike any target, no matter the skill or strength of the wielder.
On Nilfeheim swearing upon the Spear of Odin is the highest form of Oath and breaking it makes a man an Outcast and he loses all rights in the Neo Viking Society (usually is executed or killed on sight) The Nilfeheim Vikings claim they have the real mystical Gungnir and it kept in a shrine brought from Earth by the Eldest and taken to the Roundhouse for all to see during the Clan Chief meeting, during Court Procedures etc.