The Shadow Beasts (陰獣, Injū) are a special group consisting of the 10 most powerful Nen users within the Mafia organizations in the world. Under the direct command of the "Ten Dons," supreme leaders of the Mafia, every beast has his own code name that derives from the animal which inspired him to develop his Nen abilities. These warriors individually accompany the Ten Mafia Dons around the globe in their every move, but their real power is only unleashed when they are united, thanks to the fact that their abilities allow them to cover the weaknesses of each other. This group, however, ceased to exist because of the Phantom Troupe, who wiped them all out without mercy on a single night, except for Owl who was taken to be interrogated.
Yorknew City arc
After a large number of Mafia members and auction clients in Yorknew City are massacred by the Phantom Troupe, the Ten Dons send the Shadow Beasts to deal with them, not knowing who they are. After the Shadow Beasts are killed subsequently, they put large bounties on the Troupe's heads and hire professional assassins, including Zeno and Silva, to eliminate the Troupe's members.