Slender Walking is a term used to describe Slender Man's apparent teleportation, appearing and disappearing at will. As Slender Man is seldom seen walking, it can be expected that Slender Walking is his primary means of transportation and stalking his runners.
It can be seen in the EverymanHYBRID and MLAndersen0 ARGs. TribeTwelve also depicts it's own version of Slender Walking in the video, "Mary Asher Phone Call." After Noah fires a few shots at Slender Man, he is shown to quickly close the distance between them by rapidly phasing in and out of view.