Godzilla Unleashed: Double Smash is a two-dimensional sidescroller. The player controls two monsters, one on the top screen that flies, and another on the bottom screen that walks across the ground. The game is 2.5-D and moves slowly to the end of the level. Small challenges confront the player during gameplay, including human military, flying crystals and buildings. When the player comes across a crystal or building, he or she must execute a combo to destroy it. Monsters can use high and low attacks plus a beam weapon. If the blue bar on the screen is filled, the player can execute a surge attack that destroys all on-screen enemies. The bosses in the game are all unplayable with the exception of Destoroyah. Every stage in the game has two enemy monsters, a mini-boss which can be found at the middle part of the stage, and a final boss which can be found at the very end of the stage. Within the game's story mode, the game cannot be saved and the player must complete the story in a single playthrough.
Ebirah Swamps Tokyo
Orga Thrashes Sydney
Mecha-King Ghidorah Ravages Bangkok
Cairo is... Lost in Space
Atlantis Rises from the Deep
Biollante Attacks Paris
Hedorah Terrorizes San Francisco
Monster Island: The Final Battle
There are three different game modes, two of which can be unlocked by finishing the game for the first time.
- Story Mode - the only playable mode at the beginning of the game. In this mode, players will be able to battle different monsters, enemies, etc. and can uncover the story of the final boss, SpaceGodzilla. Players will also be able to unlock concept art of the monsters that they have played, and also the enemies that they have battled.
- Endurance Mode - if players obtain a B,S, or A rank, they can unlock 3D models and concept art of the different stages.
- Survival Mode - focuses on one stage. If players beat the final boss of that stage and receive an A or S rank, they can unlock monster bios and cheats, which can be used in beating the game.
- Godzilla Unleashed: Double Smash received a review score of 3.0 from IGN, who considered it "one of the worst DS games."
- Some bosses in the game are considerably bigger than their normal movie versions including Manda, Ebirah, Mecha-King Ghidorah, and Biollante. The Sphinx is also much larger in the game than it is in real life.
- The design used for Godzilla in the game is a hybrid of his Heisei and Millennium designs.
- This game features more monsters than the Wii version of Godzilla: Unleashed.
- The game's Monster Database incorrectly states that the monster Titanosaurus first appeared in the 1957 film, The Mysterians.
- The version of MechaGodzilla featured in this game most closely resembles Kiryu in design and story role, but its entry in the Monster Manifest depicts it as the Showa MechaGodzilla.
- A model of a white gorilla can be found in the game's data files.