The War Javelin is a javelin-type rangedweapon which knocks back all enemies in its path and can even be used to teleport after being thrown. This item is exclusive to the Rise of the Giant DLC.
The War Javelin can be found at the end of an obstacle course in the Cavern, next to the exit to the Guardian's Haven.
Synergies
Impaler can be used with this item to back enemies into walls and then teleport to them, allowing Impaler to crit, though this method is slightly unreliable.
The War Javelin can also be used to teleport to enemies after attacking a few times, allowing the player to initiate the fight with the later attacks of a weapon's combo.
This is usually useful for weapons which have the majority of their damage located at the last few hits, such as Giantkiller.
The War Javelin also will let slower weapons, such as the Broadsword, to get more hits of their combo in.
Notes
If the Javelin is placed in the backpack, and the mutation Acrobatipack is applied, the javelin can be thrown multiple times without being collected or returned. The teleporting function of the Javelin is also ignored.