Godzilla vs. King Ghidorah (1991) on Netflix

In this sequel to Godzilla vs. Biollante, time-travellers from the future warn that Japan will ultimately be destroyed if the monster Godzilla can't be neutralized. They reveal the circumstances of Godzilla's origin: a dinosaur who survived into the 20th Century (and who inadvertently saved a group of Japanese soldiers from American forces during World War II), only to be mutated by atomic testing on his island home. The future people have an audacious plan: to remove the pre-Godzilla dinosaur from his timestream and prevent his mutation. However, things take an unexpected turn, resulting in the creation of a new horror--the three- headed dragon King Ghidrah.