From the Super Mario Wiki
Surfing Minigame is a minigame in Mario & Luigi: Superstar Saga and Mario & Luigi: Superstar Saga + Bowser's Minions. The player can find the game in the southeastern region of Oho Ocean. There will be a green Oho Jee who will explain the rules and ask if they want to play. The game begins next to the island, with Mario surfing on Luigi. The object is to pop 23 Oho Balloons as fast as possible. The prizes for the game are awarded for the clearing time. The prizes are Chuckle Beans, Woo Beans, and Hoo Beans. If the player completes the task within 38 seconds, they are awarded the Casual Coral clothing. After that, if the score is 38 or below, the player wins two Chuckle beans, two Hoo beans, and two Woo Beans.