The source code for Gremlins Unleashed contains several hidden messages, including pictures of Gremlins characters, a shoutout to Subito Pizza and Pizza Hut from the graphists, and several profane rants.

One of the messages, resembling the Windows Blue Screen of Death, can also be found in Kirikou, another title developed by Planet Interactive.

Inside the code of Gremlins Unleashed are a set of graphics showing cameo sprites that were cut from the game for fear of legal action. In particular
• Game Boy Color boxes of Playmobil Laura, Playmobil Hype: The Time Quest, The Road to El Dorado, Classic Bubble Bobble and the Game Boy Color itself
• Dolls of Rei from Neon Genesis Evangelion, Agumon from Digimon, Pikachu, Eevee, Poliwhirl, and a Poké Ball from Pokémon, Hello Kitty, and RoboCop, as well as what appears to be the sprite artist's original characters who also appeared in Dracula: Crazy Vampire
• A book with Pikachu on it
• A statue of the presumably original character Marie Ange as an angel.