You should watch
Great Mazinger tai Getter Robo G: Kuuchuu Dai-Gekitotsu
Go Nagai crossover movie.
UFO Robo Grendizer vs. Great Mazinger
Alien invaders take over Great Mazinger who is at the entrance of a museum next to Mazinger Z as symbols of peace. Grendizer fights the evil invaders and Great Mazinger is recovered.
When the Vegan empire dispatches a new general to oversee the...
A manga comic book and anime television series by manga artist Go Nagai, made as a direct continuation of the successful Mazinger Z series. It was aired on Japan in 1974, immediately following the end of the first Mazinger series.