The Dark Tribe consists of 5 Vampires. The clan makes its appearance in Lunar Knights. Although not technically a part of the Dark Tribe, the Immortal Polidori appeared at the end of the game as the final boss, creating illusions of the Vampires defeated (and consumed) previously. He is basically the Eternal of the Dark Tribe, although his takeover was not planned.
Each member of the Dark Tribe has their own Casket Armor, imbued with the power of a Terrenial. Each terrenial holds the key to unlocking part of the paraSOL.