Mother 3 has a Combo feature called "Sound Battling", Sound Battling is done when you press the A button to the beat after the initial attack, The Beat differs for every background music playing while in an enemy encounter.
The Beat you need to follow is actually the Bass line of the music. If you can't find it, Use Hypnosis or Duster's Pendulum to lure an enemy to sleep, then listen to the heart beat noise.
The limit of attacks you can do is 16.
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