Boomerang

Boomerang is a ranged weapon which deals damage as it returns to the player.

Location
The blueprint for the Boomerang is located in High Peak Castle, next to the exit to the Throne Room. It is locked behind a door that requires the 3rd Castle Key to enter. For this the player must defeat all the Elites found in the three colored rooms throughout the level. Additionally, the player must have the Ram Rune and the Spider Rune, or the Homunculus Rune to reach the blueprint.

Trivia

 * This weapon is likely a reference to The Legend Of Zelda franchise, in which it is a recurring weapon.