Im looking for a knot that was on Mythbusters it was the knot used to shimmy up the building It only moved up the rope and couldn't go the other way does anyone know the name of it?

The practice of climbing using only ropes (not actually climbing the curface of a rock) is Prussicking (or Prusiking). The knot is a Prusik Knot or Prusik Hitch. There are various sites on the internet where the technique and the knot it self is discussed and demonstrated.