Black Augurite is a new evolution item introduced in Pokémon Legends: Arceus.
You can use Black Augurite to evolve a Scyther into Kleavor, which is one of the new Pokémon introduced in the game.
Source – eurogamer.net
Pokémon Legends Arceus – Black Augurite location: How to get Black Augurite explained
By Sarah Connor
