Technicolor mode
Enter 661334 as a code. A monster will roar to confirm correct code entry.

Black and white mode
Enter 567980 as a code. A monster will roar to confirm correct code entry.

11 lives
Enter 760611 as a code. A monster will roar to confirm correct code entry.

Indestructible buildings
Enter 112122 as a code. A monster will roar to confirm correct code entry.

Small player one
Enter 986875 as a code. A monster will roar to confirm correct code entry.

Small player two
Enter 971934 as a code. A monster will roar to confirm correct code entry.

Invisible player two
Enter 459113 as a code. A monster will roar to confirm correct code entry.

No energy gain for player one
Enter 650867 as a code. A monster will roar to confirm correct code entry.

Unlimited health for player one
Enter 677251 as a code. A monster will roar to confirm correct code entry.

Disable life and energy display
Enter 443253 as a code. A monster will roar to confirm correct code entry.

View credits
Enter 176542 as a code. A monster will roar to confirm correct code entry.

View version number
Enter 097401 as a code. A monster will roar to confirm correct code entry.

Unlock Orga
Beat the game with all characters.

Unlock Mecha Godzilla
Beat the game with Destroyah, Rodan, and Mecha Ghidora.

Unlock monsters
The other way to unlock monsters is to beat the game with certain characters.

Winning With - Unlocks

Godzilla '90s - Godzilla 2000
Godzilla 2000 - Destroyah
Anguirus - Gigan
Gigan - Rodan
Megalon - King Ghidorah
King Ghidorah - Mecha King Ghidorah

Cheat mode
Hold L + B + R (in that order) at the main menu, then release B, R, L (in that order) to display the code entry screen.

Almost all monsters
Enter 696924 as a code. A monster will roar to confirm correct code entry. All monsters except for Orga will be unlocked.

Play as Orga
At the main menu, Hold L,B,R in that order. Release them in this order: B,R,L. Then enter this as a code-202412.