The River of Flowing Sand. Monkey King, #6

Xuanzang and his two disciples were stuck at the River of Flowing Sand due to a demon with a huge "necklace" made of nine skulls. The monkey and Pigsy engaged in a big fight with the demon but could not defeat him and had to turn to Guanyin for help. It turned out that the demon had been enlightened by Guanyin. When Guanyin dispatched her aide Muzha to help them, the demon agreed to become the third disciple of Xuanzang and was nicknamed "Monk Sandy." Xuanzang was ferried across the river by the boat made from the skull necklace of Sandy and the red gourd of Guanyin.