It's a video showing a small glitch in Super Mario World. It's a very small glitch: Nothing game-breaking or really helpful here. It was assisted with save-states, but still done in real time. It just takes a few attempts and a good timing. This video was recorded in Smallhacker's hack "SMW Glitch Land". Note that no game mechanics were changed in this hack, but rather that the hack was made especially to use the glitches in SMW's original game mechanics (as well as parody other crappy hacks).