Pause Slowdown (Also known as Pause Buffering or simply Slow Mode) is a technique that is typically done with a special controller with a turbo-start button, which slows down the game by rapidly pausing and unpausing. This was first possible in Balloon Fight on the NES.
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Using this technique is easy, as it can be done by simply rapidly pressing start, causing the game to run slower and allow the players to have more time to think ahead. Some controllers have a special button that accomplishes this automatically, as with the "Slow" button on the NES Advantage controller. This technique has limited use, however, because this can only be done by Player 1, and is more likely to be frustrating than useful during a multiplayer match. The only real use would be for carefully maneuvering in a tight situation in a single-player high score run or multiplayer cooperative run.
Due to the simplicity of the technique, it can be done in any game with the ability to pause. However, because Vs. Balloon Fight and Balloon Fight for the Game & Watch have no pause function simply due to hardware, Pause Slowdown is impossible in these games.