I love watching speedruns, especially of games that I played a lot as a kid...or still do now. It's amazing how players are still finding ways of breaking some of these classic games more than two decades after they've been released. Today's topic is Super Mario World. In the video below (which I found courtesy of Polygon), speedrunner SethBling executes what's called a Credits Warp, a glitch discovered by another runner named Jeff356, that essentially let's you write and execute code within the game by performing certain actions and "wrong warping" into the ending credits.
Before you view the video, I'll just say this now. There's a lot of debate over whether something like this is considered beating the game. There are always going to be arguments for and against that notion and discussions about various categories for different games (see Ocarina of Time for an example of a game with several categories). Me personally? I just enjoy watching speedrunners do what they do best; completely destroy these games right down to their coding.