In 1991, Mullen joined the high-profile skateboarding team, Plan B Skateboards. Mike Ternasky, the owner of Plan B, influenced Mullen to transition from freestyle to street skating, and showcased his skills in the 1992 Plan B video, "Questionable". His segment begins with traditional freestyle tricks executed on flat ground, but quickly transitions into Mullen skateboarding across public terrain to shift into street skating tricks and lines. Mullen's video part signified a major transformation in relation to both his career and his skateboarding. Ternasky filmed Mullen as he sequenced tricks and mixed flip tricks with grinds and boardslides, while he also negotiated obstacles. Mullen also introduced two newly invented tricks in "Questionable", the kickflip underflip and the Casper slide.