An early concept was to have Mechgodzilla be able to split into two separate machines.
The English dub version of the movie is the only movie where Rodan is referred to by his real name, Radon.
This is the only Godzilla film featuring Mechagodzilla not to be immediately followed by a direct sequel also featuring Mechagodzilla. Gojira tai Mekagojira (1974) was immediately followed by Mekagojira no gyakushu (1975), and Gojira X Mekagojira (2002) was immediately followed by Gojira tai Mosura tai Mekagojira: Tôkyô S.O.S. (2003). The next film, Gojira vs. Supesugojira (1994), did however feature another giant robot designed to battle Godzilla, called Moguera.
Despite the film's English title, "Godzilla vs. Mechagodzilla II," the film is not a sequel to Gojira tai Mekagojira (1974). The film was retitled due to the fact that in the Western world, different films in a series rarely have the same title unless they're remakes. A third film with the same title in Japanese, Gojira X Mekagojira (2002) ("Godzilla vs. Mechagodzilla"), was also retitled for the Western market (as "Godzilla Against Mechagodzilla".)
Since the movie has a theme of "living" versus "artificial", a female pilot controlling Mechagodzilla was meant to be revealed to be an android, a human-like robot at the end. This was supposed to signify Godzilla's (living) victory over Mechagodzilla (artificial). However, since this twist seemed to come out of the blue, it was deleted from the script.
Originally intended to be a remake of Kingu Kongu tai Gojira (1962). The producers, however, considered Turner Entertainment's asking price for the rights to King Kong too high. They then planned on using Mechani-Kong from King Kong Escapes (1967), but they feared this would violate Turner's copyright. Toho ultimately decided to use Mechagodzilla, although the Mechani-Kong theme was used in the film.
On the official poster, Mechagodzilla appears with his prototype design, and doesn't look like the robot seen in the movie. This version of Mechagodzilla was meant to split and transform into smaller battle vehicles, a jet fighter and a tank, which can also be seen on the poster.
The film takes place in 1994.
Early in the film in Gojira vs. Supesugojira (1994)'s youth facility for training Extra Sensory Perception, 5 large cards can be seen on the back wall. The cards are a Cross, Star, Circle, Square and 'some wavy lines'. These are the same symbols from the ESP testing flash cards used by Ghostbusters (1984) in the film Ghostbusters (1984) albeit in a different order.