The Ghost Warriors, an army of Cursed Souls who were banished to the Cursed Realm, and serve as the main antagonists of Ninjago, Season 5: Possession.  Led by Morro, a former student of Master Wu and the Elemental Master of Wind, his main objective was to free the Preeminent, the physical embodiment of the Cursed Realm.  Ghost Warriors are constantly intangible and can pass through solid objects without effort.  Additionally, Ghost Warriors can possess various things, including inanimate objects, mechanisms, and people.  P.I.X.A.L. once detected over five hundred Ghosts aboard the Ghost's Walking Fortress.  The Ghost Army was defeated when Nya, the Water Ninja, unlocked her True Potential and used a massive tidal wave to destroy the Preeminent.