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. Also, this mode allowed to get a copy of each pet aside from creating a clone of a pet by morphing Presto into another pet and exceed the limit number of pets (maximum is 11).
- You can spawn a Star Guppy without feeding a Star Potion to a large guppy.
- The only fish that cannot be spawned is King Guppy.
- The level will be infinite if you let a fish/fishes being protected from aliens (either they are spawned automatically or by the player) or fed well. The only way to end is by clicking the Menu button at the upper right side of the screen and choosing "Return to Menu" option, buying an egg piece, and getting a game over message due to all the fishes being killed or eaten by aliens, Gash if the player spawns them many times especially if Presto is spawned as the same amount of guppies (as long as there is no other fish type) in the tank and morphing into Gash, the last fish was killed by Shrapnel's bombs, and died due to starvation.