"In 2XXX A.D. when the orbits of Pluto and Neptune exchange their positions, the Earth receives a declaration of war from an unknown planet. The invaders from Planet X attack the Earth as part of their plan to conquer the entire universe using a legion of space monsters. The Earth sends Godzilla, king of the monsters on the Earth, and Mothra, to defend itself. Godzilla advances through battle stages called Ring Fields provided in interplanetary space to battle that legion of space monsters controlled by Planet X. Godzilla must battle its way from one Ring Field to another, and finally defeat King Ghidorah at Planet X to defend Earth. For the sake of the future of the Earth, Godzilla's fierce battle now begins..."
Both Godzilla and Mothra start the game at level 1, and with a limited supply of life and power. The monsters can gain levels by defeating bosses and certain stage types (Ruins and Hyperspace); every time Godzilla or Mothra gains a level their life and power bars will increase. The maximum level is 16. The life bar will replenish once a boss is defeated, or when a Life Capsule is picked up. The power bar recovers by itself over time, and the more life the monster has the faster it recovers.
To move to the next world, the remaining monster(s) must move onto the Base Headquarters stage. On the following turn select the monster, don't move, and the game will ask if you want to advance to the next world. If either Godzilla or Mothra died before advancing, the deceased monster will reappear in the next world; however, the revived monster will lose one level as a result. Things to note: if a Godzilla or Mothra advances to the next level, and the other monster left behind is destroyed, you will lose the game. In addition, there is a chance that while exploring the levels, the player can encounter a 'Hyperspace' area. these areas feature battles against a large version of the Gotengo, Dogora cells, or Matango. Clearing these areas can reward the player with another level.
Each world hosts 2-8 bosses, depending on how far the player is, who will attack the player on their way to the enemy base. The player doesn't have to beat the bosses, with the exception of King Ghidorah, to advance in the game, but in general they will be hard to avoid and confrontation is inevitable. Things to note: boss matches (or "Hyper-Fight Mode") last approximately 40 seconds before the match is ended in a draw and both monsters are returned to the Ring Field view; in case of a draw, the enemy kaiju will have their health restored slightly (this differs between the US and Japanese version of the game).
Main BossesGodzilla: Monster of Monsters! features eight bosses, several of whom have never been in a Godzilla film up to this point. A new boss is added every world, which you will fight along with the previously defeated kaiju.
Scrapped CharactersThrough examining the game's coding and sprite data, Rodan and Anguirus have been discovered, although no sprites for them are known to exist beyond their 'pieces' for the planet boards.
Some glitches in the game can have favourable benefits to the player, while others serve only to slow them down. Gezora can infamously trap the player in the corner of the boss fight and repeatedly deal damage to them until the timer runs out. On the other hand, Moguera can sometimes get stuck in its beam charging animation temporarily, allowing the player to land more hits on the mech.
James Rolfe reviewed the game as the Angry Video Game Nerd. Although he briefly praised the simple and easy controls, he disliked the fact that the monster fights had a time limit. He was also disappointed that Mothra had weak attacks and kept falling to the floor after being hit. He also didn't like that the first monsters in the game which you fight are Moguera and Gezora, two monsters who had yet to appear in any Godzilla films, with the actual Godzilla series kaiju being introduced later in the game.