Super Mario Bros 2 player crashes the game, casually posts the clip online, and accidentally makes "the biggest 2D Mario speedrun discovery in years"

A massive new discovery in the 2D Mario speedrunning world has been made, and it's all thanks to an entirely accidental gameplay clip that a casual player happened to post online.

On March 13, a user going by Luigi's Sidekick posted a few clips on Twitter while playing through the Japanese Super Mario Bros. 2 – best known to most of us English-speakers as The Lost Levels – via the Nintendo Switch Online NES library. In one of those clips, the game simply crashes in the final level, 8-4, prompting a message from the Switch interface that "an error has occurred within the game," followed by an unceremonious boot back to the game select screen.

That was that for several weeks – until, suddenly, the video got noticed by Mario speedrunners, who recognized that it was possible for this crash to lead to lead to a method for arbitrary code execution, or ACE. This crash essentially sets SMB2 looking for code in places that it shouldn't, and by manipulating parts of a memory in certain ways – for example, by making sure enemies are in precise positions or that you have a certain number of codes – you can more or less feed the game a cheat code that warps you to the ending.

Mario speedrunner Kosmic – the same Kosmic who recently discovered that Donkey Kong's legendary kill screen isn't really the end – joked it might take a "couple... months" to break down exactly what's happening here. But if you want a "very short" version of the answer: "If you set up all of the object slots a certain way, the long firebar can be loaded in out of bounds memory," Kosmic explains. "Doing it twice can write even further out of bounds and start a chain reaction which would usually crash the game, but with extreme precision can win."

Within days of Mario speedrunners finding the crash, they'd replicated it and built out a method to use ACE to warp to the end of SMB2. Kosmic posted a clip of the warp created by fellow runner threecreepio on Twitter, calling it "The Biggest 2D Mario speedrun discovery in years." This one was tool-assisted, as it's likely far too difficult for a human to do in real time, but the community seems confident that a viable path to executing this trick for real will be found.

The catch here is that this ACE exploit only works in 8-4 which is, again, the game's final level. The trick is ultimately only likely to save 10 to 15 seconds, but that's still pretty substantial for a well-documented game like this. The old world record – which was set by Niftski all the way back in 2022 – might still be safe, however, as it's likely the game's any% category will be split into ACE and non-ACE versions if a human-viable method of doing the trick is worked out.

"I genuinely can’t believe a random crash I had with this game actually helped discover a new speed run trick," Luigi's Sidekick said on Twitter after the ACE exploit was posted. "How the hell did I do that?"

One more fun detail: the crash occurs just as Mario falls into a lava pit while colliding with a castle wall. That's the exact image that appears on the North American cover art for the original Super Mario Bros., and as some viral tweets have noted, Nintendo accidentally created some pretty incredible foreshadowing here.

It took 490 days, but the Super Mario Bros speedrun world record is now 4 frames better – and just 18 frames away from literal perfection.