War of the Monsters (1967)

unearthly monsters... with terrifying destructive powers... battle to the death... to the victor — the planet earth.

An expedition goes out to a remote island to find a priceless opal. This opal happens to be the egg of the powerful Barugon, a huge lizard-like monster that can freeze foes with its long tongue or disintegrate them with its devastating rainbow ray. When Gammera begins to fight Barugon, several plans begin to stop both monsters and keep the damage of Japan at a minimum.