The Sandbox mode can be accessed after earning either the Silver Trophy or the Gold Trophy from Challenge Mode. Entering the "Konami Code" at the main menu screen will bring the player to Sandbox Mode.
|↑ ↑ ↓ ↓ ← → ← → B A|
While in the Sandbox Mode, players have the ability to spawn any type of fish, pet or alien (excluding Cyrax). Each entity has its own corresponding key in the keyboard.
|"+" and "-"||Rotate Tanks|
The music and backdrop at the beginning will be from the last tank played in Challenge, Time Trial, or Bonus Adventure. If none have been played, Tank 1's music and backdrop will be used. If the backdrop is changed, the music will not change; it will use the last music from the last level played.
- This is the only mode where you can get all kinds of fish and aliens (also you are still obliged to kill them as they eat or kill your fishes) on any tank other than their introductory tanks. For example:
- In Tank 1, you get a Starcatcher, Star Guppy, Guppycruncher, Beetlemuncher, Breeder and Ultravore for the fish side. For the aliens side, you spawn Gus, Destructor, Psychosquid, Ullysess, and Bilaterus.
- For the succeeding tanks, this is also the same case but there is a difference. The exceptions for these respective tanks because they are introduced or appear to that tank are: Tank 2: Starcatcher, Star Guppy (needs a Star Potion to a large guppy), guppy, Destructor, Sylvester, Balrog, and Gus; 3: Guppy, Guppycruncher, Beetlemuncher, Ulysses, Psychosquid, and Balrog; and 4: Ultravore, Carnivore, Breeder, Guppy (born from breeders), Bilaterus, Psychosquid, Balrog, Ulysses, and Destructor.
- Also, you can also spawn a Star Guppy without feeding a Star Potion to a large guppy.
- The only fish that cannot be spawned is King Guppy.