The game's prototype, entitled "Parody World: Monster Party", vastly differs from the final game graphically. Most notably, the title screen featured blood instead of green slime, and many of the enemies and bosses were originally parodies of copyrighted movie characters or mythological creatures:
• The man-eating plant was originally Audrey II from the 1982 musical "Little Shop of Horrors" and shot quarter notes instead of bubbles.
• The Jack-O-Lantern was originally Caesar from the "Planet of the Apes" film series, and the background of the fight featured the famed image of the destroyed Statue of Liberty from the original 1968 film.
• The gorgon snake was originally a humanoid, most likely Medusa.
• The ghost man was originally a mummy.
• The giant spider was originally the titular antagonist of the 1982 film "The Thing".
• The giant cat-in-a-box was originally a gremlin from the 1984 film "Gremlins".
• The grim reaper was originally an alien robot resembling a Xenomorph from the "Alien" franchise.
• The vampire ghoul bore more of a resemblance to a stereotypical vampire.
• The projectiles released by the eggs in Round 2 were originally Facehuggers from the "Alien" franchise.
• The baseball catcher enemy was originally Jason Voorhees from the "Friday the 13th" franchise.
• The ghosts were originally "jiangshi": Chinese hopping vampires.

These graphical aspects were mainly changed both due to Nintendo of America's stringent censorship policy and the risk of copyright lawsuits, due to the United States' more strict copyright laws compared to Japan.