From the Super Mario Wiki
The goal of the game is to destroy a punching bag. Each time Wario hits the bag, it swings higher. After a number of hits, the bag will swing high enough to go all the way around, which is when Wario must destroy it using a finishing move. However, if Wario gets smacked by the punching bag, the microgame is lost. If Wario does not do anything, the bag detaches from its chain and rolls towards him, knocking him over.
As the microgame progresses, the punching bag becomes heavier and Wario will have to punch it more times to destroy it.
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