Submarine
From Starfy Wiki
Submarine is an ability in Densetsu no Starfy 3. As it's name implies, Starfy or Starly ride a submarine when using it. It is used to travel through pitch black areas.
Controls
The D-pad can be used to move in any direction. Pressing the A button will make a light appear for a few seconds. When the Submarine is upgraded, Starfy or Starly can shoot a bullet by pressing the B button.