Ball (Coral Coast)
From Starfy Wiki
Balls (Japanese: ボール) are four orange like balls in Densetsu no Starfy 3 that are orange with a shade of red. They are found in Coral Coast (Stage 2-4). Starfy has to push the first one (hidden behind some bark that can be destroyed by chiming Coral Bells) towards Buirun to corner him and force him to go through a door.
If Starfy and Starly do not force Buirun to go through a door and they try to enter it, they will receive the message "ボスをおいつめてから入ろう!" ("Enter after cornering the boss!"). Only the first ball is necessary to encourage Buirun to go through the door.