The Air Jump (Japanese: だぶるじゃんぷ, Double Jump) is a move that lets Starfy jump again in thin air. It is known in Japan as Double Jump, but is sometimes referred as that even in English. Only Starfy can use it. It is usually taught to him by Shurikit, but Taiblond teaches it to him in Densetsu no Starfy 4 in Flourishing Desert. To perform this move in The Legendary Starfy, players can simply press the B button to make Starfy jump and then press the B button again when Starfy is already in thin air to make him jump again. In previous games in the series, including Densetsu no Starfy 4, the A button is used to make Starfy jump instead.
Description from The Legendary Starfy
"With this move, you can jump again on thin air!"