From the Super Mario Wiki
Chopper Bros. is one of Mario's Bros. Attack during the events of Mario & Luigi: Superstar Saga. It is based off of the Luigi Dunk. The move costs five BP on Modes 1 and 2, and three BP on Mode 3. To begin, Mario hammers Luigi into the ground with the Button. They will then automatically jump to the enemy selected, but must be pressed at the right time to make Luigi jump underneath Mario, throwing him into the air. Mario can then swing the Hammer at will by repeatedly pressing the button, dealing damage proportional to how quickly the button is pressed until he lands.
Once the attack is successfully executed thirty-two times, the Advanced version is learned. In the Advanced version, Mario hammers Luigi into the ground. Luigi pops back up underneath the enemy, dealing damage, Mario hammers him back down, and the process repeats. The Advanced commands are to pound Luigi into the ground, again as the brothers near their target, and finally to make Luigi pop out and cause damage. The player should then alternate pressing and to make Luigi pop out and have Mario hammer him down again.
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