In the film, the undersea civilization Seatopia has been heavily affected by nuclear testing conducted by the surface nations of the world. Naturally upset by this, they unleash their civilization's god, Megalon, to the surface to destroy those who would — unknowingly or not — destroy them. Agents of Seatopia attempt to steal the newly-constructed human-sized robot Jet Jaguar, which they use to guide and direct Megalon. They also capture the robot's inventor, Goro Ibuki, his kid brother Rokuro and their friend Hiroshi Jinkawa. After Jet Jaguar is used by the Seatopians to lure Megalon to Tokyo and the JSDF fails to defeat it, Goro manages to regain control, and sends Jet Jaguar to Monster Island to bring Godzilla to fight Megalon. An extended fight scene then takes place, with Godzilla and Jet Jaguar, the latter newly giant-sized and self-directed, fighting Megalon and Gigan in the hills outside Tokyo. The film ends with Megalon and Gigan (who for the second time abandons an ally) defeated, Godzilla returning to Monster Island, and Jet Jaguar returning to his previous, human-sized state.
Godzilla Vs. Megalon was originally planned as a non-Godzilla film, a solo vehicle for Jet Jaguar, which was the result of a contest Toho had for children in mid-to-late 1972 (in an effort to capitalize on the many tokusatsu and anime superhero and super robot shows that were all the rage at the time). The winner of the contest was an elementary school student, who submitted the drawing of a robot called Red Arone, which superficially resembled both Ultraman and Mazinger Z (both of which were very popular at the time). The robot was renamed "Jet Jaguar" and was set to star in a film vehicle for him, titled Jet Jaguar vs. Megalon, which pitted him against Megalon (a previously unused Godzilla monster design). However, after doing some screen tests and storyboards, Toho figured Jet Jaguar would not be able to carry the film on his own, either in screen appearance or marketing value (both important to Toho), so they shut the project down during pre-production. Nearly a month later, producer Tomoyuki Tanaka called in screenwriter Shinichi Sekizawa to revise the script to add Godzilla and Gigan (especially since Godzilla had more marquee value). To make up for lost production time, the film was shot in a hasty three weeks. The production time totaled at nearly six months, from planning to finish.
Godzilla vs. Megalon was released theatrically in America on May 9, 1976, though the San Francisco Chronicle indicates that it opened there in June, and The New York Times indicates that it opened in New York City on July 11. Oddly, New York Times film critic, Vincent Canby, who a decade before had given a negative review to Ghidorah, the Three-Headed Monster - one of the more respected entries in the Godzilla series - gave Godzilla vs. Megalon a generally positive review.
In his review of July 12, 1976, Canby says "Godzilla vs. Megalon completes the canonization of Godzilla...It's been a remarkable transformation of character - the dragon has become St. George...It's wildly preposterous, imaginative and funny (often intentionally). It demonstrates the rewards of friendship, between humans as well as monsters, and it is gentle."
Godzilla vs. Megalon was given a high-profile prime-time network premiere the next year, with an introduction and bumper segments by John Belushi in a Godzilla suit.
Godzilla vs. Megalon has attracted the ire of many Godzilla and kaiju fans in the decades since its original release. The film is largely responsible for the reputation of Godzilla films in the United States as cheap children's entertainment that should not be taken seriously. It's been described as "incredibly, undeniably, mind-numbingly bad" and one of the "poorer moments" in the history of kaiju films.
In particular, the special effects of the film have been heavily criticized. One review described the Godzilla costume as appearing to be "crossed with Kermit the Frog" and another stated that sneeringly compared it to Godzilla vs. Gigan, stating that it did "everything wrong that Gigan did, and then some." However, most of the criticism is of the lack of actual special effects work, as most of it consists of stock footage from previous films, including Godzilla vs. Gigan and Ghidorah, the Three-Headed Monster, and at least one piece of effects work has garnered praise, specifically a scene where Megalon breaks through a dam.
The other aspects of the film have been similarly skewered. The acting is usually described as flat and generally poor, and as not improving, or sometimes, worsening, the already weak script. One part of the film, on the other hand, has garnered almost universal praise: Godzilla's final attack on Megalon, a flying kick. It has been called the saving grace of the film , and was made famous by the mock exclamations of shock and awe displayed on Godzilla vs. Megalon's appearance on Mystery Science Theater 3000 (Through the end of season three to the middle of season five, that clip would be shown at the opening of each show). Despite all this, the film is also one of the most widely seen Godzilla films in the United States — it was popular in its initial theatrical release, largely due to an aggressive marketing campaign, including elaborate posters of the two title monsters battling atop New York City's World Trade Center towers, presumably to capitalize on the hype surrounding the Dino De Laurentiis remake of King Kong, which used a similar image for its own poster. These posters in particular have been greeted with some embarrassment by fans.
There are, interestingly, no major female characters in the movie, making this the only Godzilla film without a female lead.
In 1976, CinemaShares released a dubbed version of Godzilla vs. Megalon theatrically. Riding the coattails of Dino De Laurentiis' big-budget King Kong, poster art showed Godzilla and Megalon battling on top of the World Trade Center, despite the fact that no scenes were set in New York City.
To obtain a G-rating from the MPAA, CinemaShares cut three minutes of footage, including:
With this being the second of the three Cinema Shares Godzilla releases, the publicity factor was high. This Cinema Shares release was the only one of the to have their Lobby Cards colored. Along with lobby cards, buttons with one of the 4 kaiju's faces on them. A couple of weeks before the release of Godzilla vs. Megalon, Cinema Shares did have a comic book released to promote the film, but in the comic there are numerous errors like monster's names and locations and events, but staying at least loose to the film. The theatrical trailer for the film also contain these errors. Such an error is Jet Jaguar being Called Robotman.
The press kit was poor also, with there being pics of Godzilla, Megalon, Gigan, and Jet Jaguar in cars. This is a reflection of the Aurora kits with Godzilla riding a race car. Along with the press kit was a vote Godzilla for president ad that if mailed in, you got a free ticket to the film.
Rhino Video (Mystery Science Theater 3000 version only)
As of April 2008, the only official English Language DVD release of the film is an R4 Australian release from Eastern Eye, which has both the US and Japanese edits of the film.