The Fly-sub is a submarine version of the Flyboat. The Pets build and fly it to save an animal in trouble that is under the water.
The Fly-Sub has the same body, wheels, lights and gears. It even looks a lot like the Space-Boat with the plastic bowl on the top. But the Fly-Sub's plastic bowl has three (3) rings drawn on it (Green,Blue and Red like the Pets' capes), that are similar to portholes. The plastic bowl has a straw on top for a periscope. The Rocket Boosters are replaced with a propeller. And when the Pets first made it, it had a figurehead of a mermaid. The second time it was a walrus figurehead and the third time it didn't have any figurehead.