A number of concepts for monsters were made for Godzilla: The Series but were never used. Many were created during pre-production of the show, and were used in promotional images and the opening credits. As they were created before any episodes had been written, many were given the names of actual Toho Company Ltd. monsters.
Named after the ankylosaur monster Anguirus from Godzilla Raids Again, this monster only appears in a single piece of concept art. It has three horns on its head, four on its neck and five on its chin.
An homage to the cyborg monster Gigan from Godzilla vs. Gigan, the Flying Gigan is a bat-like creature. It is featured in the opening sequence of the show where it is shown doing battle with Godzilla. It was also featured on a piece of promotional art for the series, battling Godzilla underwater.
Gus the Spider
Likely an homage to the spider monster Kumonga from Son of Godzilla, Gus appears at the end of the opening sequence to Godzilla: The Series. Its most notable feature is its extremely large mandibles. The Giant Black Widow in the show was based on Gus' design.
Manda the Worm
An homage to the insectoid monster Megalon from Godzilla vs. Megalon, this monster appears at the end of the opening sequence. This creature has large horns, spider-like mandibles and an armored back. It also has very skinny arms compared to its bulky body and tentacle-like hands.
Named after the mole-like robot Moguera from The Mysterians, both organic and mechanical versions of this monster appear in concept art. This art suggests that Moguera was meant to fight Godzilla and be defeated, only to be resurrected using robotics.
Bird of Prey
This creature was originally meant to be in the episode "Wedding Bells Blew." However, due to the amount of bird-like monsters already in the series, the Bird of Prey was replaced with the Sub-Zero Manta. In the Japanese version of the show, the Giant Manta Ray is still referred to as the Bird-Of-Prey.
A female Godzilla was originally meant to be in the episode "End of the Line." However, the show's producers didn't feel the need for another Godzilla in the series, so they replaced the female Godzilla with the giant komodo dragon monster Komodithrax.
- Although several of the unused monsters are named after kaiju from Toho's Godzilla films, TriStar Pictures never intended to actually license any monsters from Toho, as it would be too time-consuming with the show's tight production schedule.