The Film is heavily inspired by films like Godzilla Against Mechagodzilla (2002), SPIDER-MAN: No Way Home (2021), Godzilla vs Kong (2021), Avengers: Infinity War (2018), GODZILLA: King of the Monsters (2019), Invasion of Astro-Monster (1965), and Godzilla vs Megalon (1973).
This project has been in the planning stages since 2017 and had a very slow, but active development.
While shooting the project. Monster X wouldn't have been called "Monster X" if his name was said. In the script for GODZILLA: Across The Multiverse. Monster X was called "Kezier X" instead of Monster X. The reason isn't fully clear or have been said to why the director didn't want to call him that. But it may be said one day.
This project is said to be MZ's longest project. The title of the longest project went to GODZILLA: The Return of Mechagodzilla, with a runtime of 30 Minutes and 33 Seconds and held that tile for a year, before being taken over by Across the Multiverse. Which comes in at 49 Minutes and 10 Seconds.
It's been said that another cut of this film existed and is planned to be released in 2028. the name of the other cut is "GODZILLA: Across The Multiverse The Multiversal Cut" and is said to be 1 hour long and will have it's first showing at G-Fest 2028 and will be on YouTube later that year. However, it's yet to be fully said.