Mazinger Z vs. The Great General of Darkness

Mazinger Z vs. The Great General of Darkness , Majing Zetto tai Ankoku Daishgun? is a 1974 Japanese mecha animated film that served as an alternative link between the Mazinger Z series and the Great Mazinger series. It basically introduces Great Mazinger to the audience, as well as his enemies from the Mikene Empire, showing the defeat of Mazinger Z. It was released on July 25, 1974.

However, during a storm after a very hot day in the beach, Boss, Mucha and Nuke have a disturbing vision of a prophet that heralds the end of the world, claiming that the dead will raise and destroy the human race, and that the General of Darkness will attack from air, sea and land. The only hope of defense is an iron fortress, Mazinger. After these words, the strange figure disappears.When Boss tells these events to Koji and Sayaka, they barely credit what he says, mocking him and disregarding this prophecy as only an illusion caused by the intense heat. They start listening to music on the radio, but are soon interrupted by reports of attacks by bizarre monsters in several important cities including London attacked by Aquatic Beast Arimoth, Moscow by Reptile Beast Gurosten, Paris by Superhuman Beast Arsoth, and New York by Aerial Beast Orbee. ........

Source: Wikipedia