Mazinger Z vs The Great Dark General (1974) on Netflix

Plot summary

Dr. Hell has been defeated, so Kouji Kabuto and his friends can take a break from defending Japan and the world. On a stormy night after a very hot day at the beach, Boss, Mucha and Nuke see a prophet who announces the end of the world, saying the dead will rise and that a figure called the Great General of Darkness will strike by land, sea and air. Mazinger, he says, is the only hope. Kouji and Sayaka treat the vision as a trick of the heat. Then radio reports describe monsters attacking London, Moscow, Paris and New York. Archduke Gorgon, who has outlived Hell, watches and decides Japan is next, sending his beasts from the sea toward Tokyo. Kouji takes Mazinger Z into the city and finds enemies that speak and think for themselves.