From the Super Mario Wiki
Bonus Mission! is a minigame that appears in Yoshi Topsy-Turvy. The player has a chance to play this minigame after completing the last area of a mission and landing on Yoshi's head from a Bonus Chance! The objective of this minigame includes hitting cymbal notes a certain amount of times with a Wrecking Ball, detonating a certain amount of bombs within a specific time limit, or catching a certain amount of coins. The player can have a higher chance of playing this minigame depending on what kind of medals they obtain. If the player fails, he or she may try again until they win.