Cheat Codes:
     At  the  main  menu  highlight  "Versus" and then, in this order,
press  and  hold  L,  B, R, and then, in this order, release B,R,L. If
done correctly, a cheat menu will appear. Enter the following codes to
unlock  these  cheats.  If you entered the correct code, Godzilla will
roar.

Code:                   Effect:                        
548319                  12 Contnues in Adventrue Mode
154974                  Add A.I. Player to Melee
107504                  All Cities 
863768                  All Cities and All Monsters
962129                  All Gallery Items
209697                  All Monsters
600225                  All Monsters Are Invisiable
154974                  All Players Are Small
817683                  All Players Deal Quadruple Damage
569248                  All Players Take No Damage
860475                  Black and White Mode
440499                  Boxing Ring
778393                  Constant Energy for Player One
881557                  Constant Energy for Player Two
597558                  Constant Energy for Player Three
218967                  Constant Energy for Player Four
352117                  Destoroyah
880460                  Disable HUD
097401                  Display Game Version Number at Option Menu

Unlock Hints: 

Get King Ghidorah: Beat Adventure mode with Megalon.
Get Gigan: Beat Adventure mode with Angilas.
Get Destroyah: Beat Adventure mode with Godzilla (Millennium).
Get Rodan: Beat Adventure mode with Gigan.
Get Mechagodzilla: Beat Adventure mode with Rodan.
Get Mecha-King Ghidorah: Beat Adventure mode with King Ghidorah.
Get Orga: Beat adventure mode using all characters then beat
          the adventure mode one more time using Godzilla 2000. 

Unlock Pictures In Picture Gallery:
     To  unlock  pictures  in  the  Gallery,  you  must  play  through
Adventure  Mode  on  the  Medium  or  Hard  difficulty  setting.  Some
buildings  that  you  destroy  will  reveal Silver Atari symbols. Pick
these up to unlock a picture.