From the Super Mario Wiki
10-Point Star is a collectible item that the Yoshis can use in Super Mario World 2: Yoshi's Island, and its remake, Yoshi's Island: Super Mario Advance 3. It can be obtained by winning certain minigames. It is worth 10 Stars, giving him 10 more seconds for the Countdown Timer. There is also a similar version of a 10-Point Star called a 20-Point Star.