Gungnir is the spear of Odin. If the party successfully survives nine turns of the Jotunn invasion during Charge of the Einherjar, you find that Grimnir has hung himself to the close to the camp with the spear impaled in his body. The spear can be removed from the body and be used until the end of the game.
Gungnir is a high-quality spear with the unique ability that all characters in its path will be hurt by its attacks, with the ability to bypass blocking if the wielder has a shield. This means you can inflict damage on two enemies with one attack. But allies or party members will suffer damage as well in case they are in between the target, so this unique ability is a blessing and a curse.
In case the wielder has the venomous Status effects, that will be applied to its targets as well. If a build is needed for a character to get the best results with this weapon, see Odin's chosen warrior.
In case the wielder use Charge, enemies may block this attack.
Maximusing amount of attacks and effects in a single turn
The amount of attacks in a single turn can be boosted by the Inspire ability from the leadership skill tree. The amount of attacks can also be increased by equipping Kyre's Charm and having the passive skill Relentless.