Causes Dusclops to evolve into Dusknoir when traded while holding it. This consumes the Reaper Cloth. In Pokémon Legends: Arceus, due to the absence of held items, the Reaper Cloth simply needs to be used on Dusclops to trigger the Evolution.
In Pokémon Conquest, Dusclops evolves into Dusknoir if it knocks out a Warrior's Pokémon in a manner that allows recruitment while its own Warrior is equipped with a Reaper Cloth.
Reaper Cloth can be purchased from the traveling merchant for 5000 gold, and sold for 2500-3250 gold.
A Reaper Cloth appears as a held item on the Secret WondersDuskull card. It allows Duskull to evolve on the turn it is played. This contrasts with other media, in which the Reaper Cloth allows Dusclops to evolve into Dusknoir rather than Duskull to evolve into Dusclops.
Trivia
The song Ghost Dive references the Reaper Cloth in its lyrics.