Yūrei[1] (幽霊 or ゆうれい) is an enemy in Wario Land 4 in the level Crescent Moon Village. Yūrei can't actually be hurt or defeated by Wario since he is a ghost, he however, can't hurt Wario either. What he really does is steal Keyzer, the ghost that Wario needs every in order to advance trough the game and loose change on the ground, he will steal any type of coin, but will not steal gems or coins that float in the air. Yūrei only makes two appearances in the level, on the long outside areas.
His name refers to figures in Japanese folklore that are analogous to Western legends of ghosts.