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does anybody know how to overclock AND underclock your gameboy so you can make it variable?

I have a gameboy that I overclocked
and I underclocked a game boy. with positive results and they work great!
i also circuit bent my guitar effects pedal
and I've seen a video on youtube of a guy who used a 555 timer to help the game not crash
and a variable resistor. http://www.youtube.com/watch?v=ypmBP_Pt1Bg

i can't figure it out