The Skull of Hazza D'ur is the secondary antagonist of Season 13: Master of the Mountain of LEGO Ninjago: Masters of Spinjitzu. It is an ancient demonic skull that is used as Vangelis's main weapon. It assists the Skull Sorcerer in battle against the ninjas, and it is also responsible for bringing the Awakened Warriors to life.
The skull once belonged to an evil sorcerer known as Hazza D'ur. When the sorcerer was defeated, the skull temporarily lost its powers and went into a deep sleep, which seemed to have lasted for a few years until the day Vangelis ordered his minions to retrieve it for him. Later, Vangelis betrayed them and revealed his true intentions to use the skull for his own evil purposes. The skull first appeared when the Skull Sorcerer came to punish the munce and geckles after being alerted by the Awaken Warriors. Throughout the season, the skull gives advice to Vangelis on what to do in case the ninja try to escape the dungeons or try to assist the munce and geckles in learning how to get along with each other. The skull was later eventually destroyed during the battle between Cole and Vangelis.
The skull is quite cruel, as it seems to like taunting it's enemies. It is also helpful to Vangelis, giving him instructions and advice on what to do. The skull is implied to follow its master's orders without question. The skull also has a tendency to repeat the same thing its master says.