From the Super Mario Wiki
Ground-Pound Pop is a two-player minigame in Yoshi's New Island. The objective of the minigame is to pop as many target color balloons by ground pounding in one minute, with the target color being displayed at the bottom screen, as well as the next color. A Yoshi starts the minigame in a castle-like area with the target color changing after a few seconds. Balloons also appear at various intervals, and the player who gets the most points at the end is the winner, with each balloon awarding ten points. The balloons come in three colors: red, blue, and yellow.