How is sha wujing changed by the journey to the west?

By making a left istead  of a right and got lost 

In this classic 16th century Chinese novel,Journey to the West, there are four primary characters:  Xuanzang, Sun Wukong, Sha Wujing and Zhu Bajie.

Xuanzang, the main character, is a monk who is sent on a pilgrimage.  At the end of his journey, he achieves Buddhahood, which would be described as the perfection of knowledge and wisdom.

Sun Wukong, is a disciple in the form of a monkey.  His reward for his part in the journey is an arhat, which is an acknowledgement of worthiness.  It is one step below Buddhahood.

Sha Wujing is a river ogre who must gain atonement for his transgression. His final outcome is to become a deity known as naga.  Commonly, naga is represented as a great snake or cobra.

Finally, there is Zhu Bajie, a creature of great lusts and appetites.  He is represented as a pig.  Fittingly, his reward is to become an altar cleanser.  He is responsible for cleaning up excess offerings left at Buddha’s altar.