Doraemon: The Record of Nobita's Parallel Journey to the West(1988)

As Nobita, Shizuka, Gian, and Suneo are auditioning for a role in their school's play based on "Journey to the West", the coveted role of Son Goku is hotly contested. After suggesting that the real Great Sage Equal to Heaven should play himself, knowing that the story is only a legend, Nobita and Doraemon go back in time to find their own fake Monkey King, but arrive in present day with the story's demons having taken over the world. The only way for things to go back to normal is for Nobita and pals to reenact the tale...for real!