"Rub" the urn 3 times. The third time, a mob of djinn will spawn, including 2 Sapphire Djinn, 1 Ruby Djinn, and a Djinn Overseer (an upgraded Ruby Djinn). The Overseer can do massive damage, around 300 damage per attack. Once you have killed all 3 lesser Djinn and weakened the Overseer (reduced its health to <25%), the Overseer will become neutral. Speak to it to continue the quest. Mabai will disappear; find him in the Halls of Chokhin to complete the quest.