I'm King Kong!: The Exploits of Merian C. Cooper

Controlled from the mysterious tenth planet, the immensely powerful Giant Demon Beast! The Earth is in danger! Launch the counter strategy, Gamera, you can do it!

Two young boys sneak aboard a spaceship and find themselves whisked away to the mysterious planet Terra. There, they encounter Gamera's old foe Gyaos and two female aliens with a taste for human brains. Gamera must save the children and battle the new monster Guiron, whose entire body is a deadly living weapon.