Arguably one of the most famous speedruns of all time is Narcissa's 22:38 run of Zelda: Ocarina of Time at Awesome Games Done Quick in 2013.
For the uninitiated, Narcissa's run was evidence of how much one of the most acclaimed video games of all time could be broken down and manipulated. From 2013 up until very recently, the same route used by Narcissa more or less remained the optimal path for finishing Ocarina of Time as fast as possible.
Within that time, the world record for the Any% category (simply finding the shortest route between the start of the game and its end credits) was shaved down to just over 17 minutes. Now, thanks to a new combination of glitches, 16-year-old runner Lozoots has completed the game in 12:59, cutting more than four minutes from the previous world record.
The first discovery that led to this run being possible was of a glitch called Stale Reference Manipulation (SRM.) This is essentially a method to change the contents of a chest from its intended item to a wholly unrelated item by inputting a precise series of commands.
From SRM, a trick called Arbitrary Code Execution (ACE) was extrapolated, since the speedrunning community correctly assumed that more could be altered than just the contents of chests. Essentially, players can now program code that can cause new effects than what is otherwise coded in the game, simply using controller inputs. Reddit users CStock77 and Ballistix_Gaming both explain ACE in layperson's terms in a thread introducing the discovery of the application of ACE to Any% speedruns.
Lozoots' world record run resembles the previous optimal route for the first nine minutes or so. It first requires using a glitch to obtain the ocarina from Saria on the bridge outside of Kokiri Forest before getting the sword and shield using the intended method (as quickly as humanly possible, of course). Then, once the slingshot is acquired from inside The Great Deku Tree, the game is reset and the run becomes unintelligible to those outside of the OOT speedrunning community (and maybe even to some of them too). What ensues is more than three minutes of precisely timed button presses that results in an instantaneous warp from Kokiri Forest to the end credits.
Since the Credits Warp trick was first shared by MrCheeze (after being discovered by glitch hunters in the Ocarina of Time speedrunning Discord community) Lozroots has posted three world record runs, besting their previously-shared times twice. 12:59 remains the world record now, but given the newness of the Credits Warp trick, that record may very well be bested by Lozroots yet again or even a new entrant into the fray in the coming days.
Source: Lozroots, r/Speedrun