Speedrunners tend to break games. Then they take the broken pieces and glue them back together in a fashion that lets them finish the game faster. Super Mario World has been picked apart so thoroughly that runners can warp straight to the end credits from the first level.
The current world record holder SethBling has made a detailed video showing just how Super Mario World speedrunners manipulate the game's memory to achieve this.
The video renders Super Mario World's memory as grayscale pixels alongside gameplay footage. As SethBling executes an item swap glitch he explains how the game reads and writes different parts of the memory until it jumps to what he describes as "open bus".
From here SethBling has more control over what is happening to the memory and goes through a series of precise, pixel-perfect movements in order to manipulate the memory to the right values needed to trick the game into skipping to the credits.
There's a fascinating science to how all of this is handled. The memory manipulation and glitch usage go to the point where speedrunners aren't even playing Super Mario World anymore. They're doing something else that just happens to use Super Mario World as the starting point.