Super Mario Bros. 3 in 3 minutes - World Record Speedrun Explained

you may have seen the speedrun of super mario brothers 3 that completes the game in just about 11 minutes the general route is pretty simple gather two warp whistles from these two stages in world 1 use them together to go directly to world 8 then get through that world and defeat bowser but even a straight line isn't always the shortest path sometimes the shortest path is through a wormhole on august 1 2020 zakubi achieved the seemingly impossible feat of beating the game in 3 minutes and 2 seconds this is the super mario brothers 3 any percent speedrun explained [Music] the first 2 minutes are very similar to the any percent no wrong warp run by mitch flower power zakubi gathers p-speed early in this level and blasts through it with ease [Music] [Applause] [Music] notice how the hammer brother moves only once at the end of the stage this will be the case for all four hammer brother movements in the run this optimal pattern which only has a three percent chance of happening is required to get such a good time but the first hammered weather movement was actually manipulated this game's random number generation function runs on every frame and always goes through the same sequence of numbers as a result any random element can be manipulated by having it happen on a specific frame by waiting on the title screen until this exact time the qb set up the hammer brother to move by only one tile as long as he finished 1-1 within a 5-frame window after that it becomes too difficult to finish levels with this kind of accuracy so the remaining movements are essentially random this does bring up the chance of optimal movements from 3 to 6 assuming the manipulation is done right quick side note in my previous video i made a mistake with the odds of each direction of a t-shaped intersection all of the percentages in this video have been corrected to reflect the actual odds [Music] in this level he does the same strategy of reaching p-speed on the pipe then tries to get mario to run down slopes as much as possible [Applause] mario runs about five percent faster down slopes with a speed of up to 59 compared to 56 on flat ground over the course of the level running down slopes saves about 3 or 4 frames [Music] [Applause] [Music] here the strategy is again identical to the no wrong warp run zakubi needs a mushroom to get the super leaf in the next level and he needs to wait four seconds on this block to reach the secret exit and get the first warp whistle [Music] now all jakubi needs is the second warp whistle from this fortress's secret exit which he flies up to using the super [Music] leaf [Music] here though he doesn't go into world 8. instead he goes into world 2 then warps to world 7. why do such a thing well let's see what happens [Music] [Music] me [Music] and that's it that's the run so what happened in short mario hit a glitched note block and the game crashed in the perfect way to make it immediately load the ending sequence to help better understand why i painstakingly recreated the run frame by frame on emulator the result very closely matches the original and will let us analyze all the variables at play first mario hit the side of this pipe and entered it in the wrong direction with enough speed mario can sometimes move into solid blocks he can usually only stay inside of a block for a single frame after which he's pushed out but by clipping inside of the pipe at this spot he's also standing on a pipe exit tile normally because pipe exits are always connected to a pipe mario can only go in them from one direction so nothing was made to specifically prevent mario from entering them the wrong way so by pressing down against the top of the pipe exit tile mario goes down into it instead of up when mario's traveling in a pipe he simply moves along the pipe until he reaches another exit tile at the other end however in this case there's no other end so mario keeps going down this glitched pipe until he leaves the bounds of the level map so where does he end up well this is where it gets complicated the level data is divided into up to 16 screens ordered from top to bottom in vertical levels the game uses a table as sort of a reference sheet for any given screen the table holds the memory address of where the level data for this screen is located when mario reaches the 17th screen there's no more level data so the game starts to look beyond the table to find the memory address the address found is garbage data which is a value used for a completely unrelated purpose that makes no sense when used as a memory address for level data the game then goes to the wrong place and finds more garbage data that it interprets as if it was level data so the end result is a garbled mess to make things worse tiles are drawn on screen through a separate process that also goes horribly wrong so the garbage on the screen is different from the garbage that is actually there mario keeps going through this mess until luckily at the top of the 19th screen the garbage data happens to line up so that there's a tile that acts like a pipe exit and frees mario from the glitched pipe on the right edge is the culprit for the whole game crash an invisible note block the animation when mario bumps a block is more complicated than it looks blocks are background tiles which are generally incapable of being animated in this way to get around this limitation the background tile is removed during the animation and replaced with a sprite that removal is what causes the crash super mario bros 3's rom is 8 times larger than what the nes can load instead of loading it all at once the rom is subdivided into 32 banks that can be swapped in and out of memory so that only four of them are loaded at any given time the memory address for the 19th screen happens to point to a location that's normally used to control which banks need to be loaded normally only the middle two are ever swapped out the first one is always bank 30 and the last one is always bank 31 but when the game attempts to remove the note block tile for the bumping animation it swaps out these two banks instead replacing the very code it's currently running for a different part of the rom this causes one of the key elements of the nes processor to fail the stack instructions in the code are organized into multiple layers of routines and subroutines so that any given basic function has its associated routine that can be called from any point in the code when jumping around between subroutines the processor needs to remember where it came from so that it can go back there after it's done this is what the stack is used for the stack is essentially a list of return addresses in reverse chronological order whenever a subroutine is called the memory address where the call was made is added to the stack and when a subroutine is done the processor returns to the address at the top of the stack to go back where it came from typically the number of return addresses in the stack matches the number of layers in the subroutines the processor is currently in however in this case because a different part of the rom was suddenly loaded in this balance is thrown out of the window after swapping out the rom banks the processor starts running code from inside a subroutine at the end of which is an instruction called return from subroutine so the processor looks at this stack and finds only one return address so it goes back to that address clears it from the stack and resumes executing code from there but because the wrong bank was swapped for a new one the return address no longer points to where it was supposed to instead it points to yet another subroutine which ends in the same instruction returned from subroutine the problem is there's nothing in the stack to return to anymore this is called the stack underflow as it tries to find the return address the processor loops back around to the other end of the stack super mario brothers 3 doesn't make use of all 128 entries in the stack so the last entry is instead used for other purposes specifically it's made up of two variables one for the status bar mode and one for the level mode for a vertical stage they take up values 0 0 and 8 0. this means that 0 0 8 0 is used as a return address to continue executing code this leads directly into these variables when executed like code they're ordered in this way the first byte is a code number for an instruction and the next two bytes are parameters given to that instruction usually a memory address let's look at this instruction it's made up of the horizontal position of enemy slots 3 4 and 5. this is interesting because all three variables can be manipulated to any value we want as long as the right enemies are placed at the right location this means that any code instruction can be executed here as long as the enemies are in the correct horizontal position but surely you can't have three different enemies move into pixel perfect positions right yes you can because that's exactly what zakubi did first the enemy slots were manipulated by killing the piranha plants while moving up in the level and loading the enemies in the correct order so that sloths 3 4 and 5 are taken up by these three koopas zakubi kills the koopa in slot 4 on this block which puts it at position e3 next he flips the koopa in slot 3 and goes down the pipe when it's at position 2-0 this pipe entry has a two-frame window for the position to be correct it's interesting to note that this part did not go as intended zukubi turned around slightly too early here which threw off his usual method of tiling the pipe entry right to compensate he didn't turn back to avoid overshooting the pipe and winged it for the timing luckily for him it worked and the shell was correctly stopped at position 2-0 finally he carries with him the coupon slot 5 all the way down to the 19th screen where he throws it to the left on the frame where its position is at 9 5 zakubi jumps activating the crash and leading the code to read the instruction 2 0 e3 8f 2 0 is the code for a jump to subroutine instruction this instruction essentially makes execution jump to the address specified by the next two bytes so execution moves to 8f e3 which would normally be the function that loads the ending sequence but remember after the wrong bank was unintendedly swapped for another the ending sequence can no longer be found at 8f e3 except very conveniently for us one of the things that this instruction does is to swap the wrong banks back to their intended positions which means that the ending sequence is put back in its place just in time to be jumped to so after all of these unintended hoops and hurdles the game finally jumps to the end and princess speech is rescued many things can go wrong though before reaching the jump instruction the code runs through other variables so they need to have values that translate into code that doesn't crash or derail execution for example the horizontal position of this koopa is used as an instruction as well in this run zakubi was fast enough so that the koopa de-loaded with a horizontal position of 7-4 if he had been 2 frames slower the koopa would have had a position of 7 2 instead which translates into an instruction that instantly stops execution five of the 11 most common koopa positions would result in the trick failing on top of that the sound engine also runs into its own issues in short the sudden jump to the end sequence deletes the music data that the sound engine was reading which causes it to get caught in the loop depending on where the music was before the jump the processor can eventually exit the loop and play this glitched sound or it can get stuck for longer and delay the ending [Music] or even worse eventually hit an instruction that tells it to quit all execution here's a quick recap mario clipped partially inside of this pipe which allowed him to take it down instead of up this glitched pipe has no exit so mario goes down until he's beyond the bounds of the level and into garbage data where a note block can be found interacting with an out-of-bound snow block causes the game to go through a series of unintended jumps in its code that eventually leads it to read the horizontal position of enemies as if they were instructions of game code through careful manipulation they are set to values which translate into a simple instruction that tells the game to load the end screen so that's what it does and the game is beaten this way the run itself is so close to perfect that with this current strategy even a 301 seems very unlikely zakubi only lost 11 frames on the overworld a few frames entering the secret door in the fortress and a couple more in 7-1 keep in mind though that improving a stage by a frame or two most likely would cause the hammer brother to go the wrong way because of that there are only a few select frames where a stage can be completed to get optimal patterns making slide improvements even harder to come by the tool assisted speedrun uses a completely different and faster setup that makes use of a piranha plant to replace one of the koopa shells but good luck replicating that with the controller as of right now as close as it is a time of sub 3 minutes looks to be humanly impossible to achieve if you want more in-depth information about what goes on in the game's code during the wrong warp please watch this video by retro game mechanics explained although slightly outdated by now it was the most vital piece of information i had when making this video and a lot of the visualizations were based on isoop frieza's incredible work so i want to thank him for making it as well as helping me troubleshoot a few things also more detailed explanations of the sound glitch and other internal mechanics written by cab audio can be found in the video description thanks for watching [Music] you

Channel: Bismuth

Views: 483,869

Rating: 4.9568186 out of 5

Keywords:

Id: WWbZFj-cLvk

Length: 15min 51sec (951 seconds)

Published: Sat Sep 12 2020

Reddit Comments

[u/fiddich1]

How on earth do people figure things like this out?

[u/Kenban65]

I was more impressed when Mitchflowerpower did this live on the late show a few years ago. It’s an impressive feat because it requires extreme precision to pull it off at all, but doing it live on TV with a good chance of screwing it up is amazing.

https://m.youtube.com/watch?v=jvLwpnn1F4Y

[u/IroncladDiplomat]

How many half A presses required?

[u/adm_shiza]

someone tell summonsalt someones stepping on his turf.

[u/rawj5561]

This is insanely cool

[u/FormalFistBump]

If the whole glitch happens because he jumps into a downpipe, could he not have jumped into one earlier than Level 7? Or is Level 7 the quickest way to get to a downpipe?

[u/Gashcat]

"Can't really be replicated with a controller" It will happen. Every time we think something can't be replicated by a human, speedrunners, uh, find a way

[u/QuarterFlounder]

This guy makes me feel like an idiot, yet I found this video completely fascinating. I love how complex speedrunning old games has gotten.

[u/totallyanonuser]

well...that is the best way i've seen a speedrun completed. ever.

wonder what trick they'll figure out next for sub 2min (you know someone will)