- Executive Meddling: Originally it was going to be Baragon, Varan and Anguirus going against Godzilla, but the latter two were swapped out for more popular monsters (Mothra and King Ghidorah, though they were nerfed) because Toho did not believe Anguirus and Varan were marketable enough. Baragon however, was kept around due to his huge fanbase in Japan (in contrast, while Anguirus is a fan favorite amongst Western audiences, his popularity is only so-so in Japan).
- Fan Nickname: Guardian Ghidorah, Spirit Ghidorah, or GMK Ghidorah, for this version of King Ghidorah.
- The Other Darrin: Mizuho Yoshida replaces Tsutomu Kitagawa as the suitman for Godzilla this time around.
- Production Posse: Director Shusuke Kaneko, special effects director Shinji Higuchi and composer Kow Otani have previously worked on the Gamera Heisei trilogy.
- Technology Marches On: The entire nonsensical "rocks and stones are like the CDs of the dead" exchange.
- Theme Music Withholding: The classic Akira Ifukube "Godzilla March" isn't heard until the final Wham Shot of the film.
- What Could Have Been: The above executive meddlings and Godzilla was originally going to walk with his tail more parallel to the ground but it was a strain on the actor's back so his posture went back to normal.
- Before settling on the initial idea, Kaneko optioned to have Godzilla fight Kamacuras. He was very interested in using advanced special effects techniques, including lots of CGI, to breath new life into the mantis design. It was scrapped due to Godzilla vs. Megaguirus being in production, and Kaneko wanting to do something more original rather than creating a film with similar opponents.
- The movie was originally supposed to have been released in March 2002, but for unknown reasons, this idea was dropped, and instead, it got a December 2001 release date.
- Next, Kaneko fleshed out a story in which Godzilla does battle with an astronaut turned space alien dubbed "M". A couple of drafts for the idea were worked on, the last one created made full use of the Millennium concept with an alternate reality where Japan had become the "Republic of Japan" with a large military at its disposal rather than a Self Defense Force. In the end however, Kaneko dropped the story because it ended up being too depressing for the kind of movie he wanted to make.
- TriStar was VERY close to giving the film a new dub job and a limited nationwide theatrical run like Godzilla 2000, so far as coming up with a new English title, Godzilla Must Be Killed! (or abbreviated as GMBK, for "Godzilla, Mothra, Baragon, King Ghidorah"), but for whatever reason, the plans fell through.
- Godzilla was originally going to fight smaller, weaker monsters who were sent as guardians to save Japan from his wrath and writer Shusuke Kaneko first selected Anguirus, Varan and Baragon. Toho disapproved of using Anguirus and Varan because those two haven't brought on big numbers at the box office in the past (even though Anguirus never got his own movie) and for a real stupid reason, not luminescent enough. The costume designer for the movie was so upset that Toho declined to let Varan appear (as Varan was his favorite monster) that he put some of Varan's skin onto King Ghidorah.
Trivia / Godzilla, Mothra, King Ghidorah: Giant Monsters All-Out Attack!