Below is a complete list of all the differences between the US and Japanese version of Godzilla: Monster of Monsters!

Game Names
The Japanese title of this game is simply Godzilla, or Gojira, while the US version goes by the longer title Godzilla: Monster of Monsters!

Title Screens
Both versions have distinct title screens from each other The Japanese version has a shot of the Mosugoji suit, from Mothra vs. Godzilla (1964) and Ghidorah the Three-Headed Monster (1964), with Japanese text above which says Gojira, while the US version has a shot of Godzilla's back with English text which says Godzilla: Monster of Monsters!

The US version removes all mention of "Toho Cenfile-Soft Library" and "Compile," and instead credits "Toho Eizo" on the title screen.

Movement
The monsters movement on the hexagon maps is quite different for both versions:

US version
Godzilla can move up to 2 spaces
Mothra can move up to 4 spaces

Japanese version
Godzilla can only move 1 space, or 2 spaces if one of them is a Sub Space level
Mothra can move up to 2 spaces

Boss Regeneration
Bosses in the Japanese version have increased regeneration rates. For example, Gezora on Earth regains 1/5 a bar of health each turn in the US version, while in the Japanese version he regains a full 2 bars of health each turn.

Starting Health - Gezora
In the US version, Gezora starts with 4 bars of health/power
In the Japanese version, Gezora starts with 5 bars of health/power

Music
Two of the music cues present in the Japanese version have been replaced with music that appears later on in the game for the US release. The first is the title screen music, which in the Japanese version is Akira Ifukube's Godzilla March, the other is the intro "cinematic," which in the Japanese version is Ifukube's The Great Monster War March. Note, these two cues do appear in the sound test, at 00 and 01, for both versions.

Monster Names
Several of the monsters have different names between the US and Japanese version, below is a complete list:

Gezora
Gezora (US version)
Gezorah (Japanese version)

Moguera
Moguera (US version)
Mogela (Japanese version)

Baragon
Baragon (US version)
Varagon (Japanese version)

Hedorah
Hedorah (US version)
Hedrah (Japanese version)

Mechagodzilla
Mecha-Godzilla (US version)
Mechagodzilla (Japanese version)

King Ghidorah
Ghidora (US version)
KingGidrah (Japanese version)

Turn Order
In the US version, the lower level monsters will move first. In the Japanese version, the higher level monsters will move first. For example, in the US version, Gezora would move before King Ghidorah; however, in the Japanese version, King Ghidorah would move before Gezora. As a result, in the Japanese version enemy Kaiju are usually more congested around the world's exit as the higher level monsters won't be able to move right away with the other monsters blocking their path.

"Cinematic" Scenes & In-Game Menus
Naturally, all text from the "cinematic" scenes and in-game menus, where you give commands to monsters, will appear in English on the US version, and in Japanese on the Japanese version.

High Score
The US version of the game adopted a point system, or a player's score, in that you receive points according to the amount of damage you deal, and are dealt. The Japanese version is devoid of a score system.

Passwords
The same passwords work for both versions, and English is used for both as well, the difference between the two versions is that the Japanese version is color coded, in that letters will appear white and numbers in red. In the US version, the 0 has a slash through it to tell it apart from a O.

Sound Test
The US version has a larger sound test, activated with S0UND as a password, than the Japanese version. While the Japanese version stops at track 25, the US goes up to 47; however, tracks 26-47 are sound effects from the game.