Revealing mistake: Near the beginning, Megalon steps out from behind a mountain. It's obvious the "mountain" is a cardboard cutout.
Godzilla vs. Megalon (1973)
Ending / spoiler
Directed by: Jun Fukuda
Starring: Katsuhiko Sasaki, Hiroyuki Kawase, Robert Dunham, Yutaka Hayashi
Genres: Sci-fi
Godzilla, with the help of the robot Jet Jaguar, defeats Megalon and Gigan and stops the civilization of Seatopia from carrying out its diabolical plan.
Alex
More mistakes in Godzilla vs. Megalon
Trivia: The weapons used against Megalon (the ones that look like satellite dishes that shoot lightning) actually existed, although they were never used in combat. The Japanese experimented with them during WWII.