Godzilla vs. Mechagodzilla (1974) starring Masaaki Daimon, Kazuya Aoyama, Akihiko Hirata

Aliens intend to take over the planet. Just in case Godzilla tries to interfere, they’ve built a mechanical version of him to put an end to his interference. The Earth humans summon the legendary King Caesar to assist Godzilla in the battle.