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Over a year ago, an ordinary player stumbled upon a crash while playing the Japanese version of Super Mario Bros. 2 on Nintendo Switch. In itself, that's not such a wild thing – even old games crash now and then – but the specifics of this glitch turned out to have massive implications for the speedrunning community. This ended up being the first step in essentially reprogramming the game as it runs to do anything you want, and now, after a year of work, speedrunners have applied those lessons to the original Super Mario Bros. as well.
This glitch is a door to arbitrary code execution. ACE exploits take advantage of bugs in a game's code to input new instructions that were never intended by the original developers, opening the door to all kinds of wild shenanigans. Speedrunners, for example, might use ACE to warp directly to a game's end credits.
The specifics of how it works are far too complicated to detail here – there's a reason Kosmic's video is over an hour long – but in essence, it involves making sure certain enemies are loaded into the game in a particular order all at the same time. Once the crash was uncovered, it was relatively simple to replicate it in the Japanese Super Mario Bros. 2, where all the proper ingredients come together in the game's normal final stage, 8-4.
It was not nearly so easy to find a spot in the original Super Mario Bros. where the same ACE exploit could be performed. In fact, no such place exists, at least in the game as it was intended. So, the only way to find all the necessary enemies in place is to go to the infamous, glitched Minus World in – specifically – the Famicom Disk System version of the game.
But even that's making it sound too simple, because Kosmic and other runners spent the better part of the past year trying to figure out the exact combination of actions to get ACE working. One member of the community, 100th_Coin, had to rewrite existing NES emulators because they weren't accurate enough for testing.
So what's it all entail? Well, you need to beat the game once through the Minus World to unlock the second quest, which turns all the Goombas into Buzzy Beetles. Then you restart the game, die as fast as possible as Mario, then run to the Minus World as Luigi, collecting power-ups along the way. In the Minus World, you need to move past the flagpole, kill the first Bowser you see, manipulate a particular Buzzy Beetle to run to the right, and stay on the ground until another Bowser loads.
All together, that causes the game to skip out of normal code execution to start reading code from the PPU, the part of the NES that actually draws the graphics you see on-screen. "We make sure the data here at this exact moment gives us the right value," Kosmic explains, "and we do this by using the height of the Blooper on screen. This makes a one-byte, or in other words a very small, change to the game, which will remain when we hit reset. This change corrupts the routine of powerups. So when they come out of blocks, we get a jump to RAM. And from here, we're kind of home free. We can control what instructions the game runs because we can control what numbers are in memory when it arrives here."
As a speedrun trick, it's not particularly useful, as it actually takes longer to do the ACE exploit than it does to beat the game normally. But that's not really the point – the real goal here is just to expand the bounds of what's possible while playing Mario. "We can make Mario swim in the air," Kosmic says. "We can do whatever we want. The point of ACE is that it's awesome. At the end of the day, it's not meant to compete with regular runs. It's just amazing that it works at all."
This is, after all, what speedruns are all about – at least in my mind. Beating games quickly is just a byproduct of the real work, which is breaking the constraints of those games down as far as they'll go and figuring out what's possible as more and more barriers start to disappear. Even now, 40 years later, it's astonishing to know Super Mario Bros. still has some secrets left to discover.
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