Starly (Stapy in Japan) is a character in the Legend of Starfy series of video games. She is Starfy's sister in the series, and would become a playable character in her first appearance, The Legend of Starfy 3. She is the royal princess of the Pufftop Kingdom. She's a hyper character in the series who's also considered rude (though not as much as Moe is).
It should also be noted that, when playable, she is very different from Starfy. So far she has been a playable character in the third, fourth, and fifth video games in the series.
In The Legendary Starfy, she can be played by another player via Nintendo DS Download Play or by anyone else who owns their own copy of the game. Starly and Starfy will play along-side each other, while Starly uses different moves that Starfy cannot learn. In the levels of The Legendary Starfy, she has a wall-jumping ability that allows her to get to high-up pearls, for health/money for the person whom invited the player to play as Starly.