A short emulator-aided demonstration of how the broken ladder glitch works (not shown: the dozens of frame-perfect inputs needed to pull it off).
Better to be lucky than to be good
While players have theorized about using the broken ladder glitch to pass the kill screen for years, it initially seemed like even this glitched shortcut was too slow for the short kill screen timer. Yet when Kosmic attempted the same trick using his own emulator-assisted setup recently, he says he was able to complete the level on his first try. What gives?
As it turns out, Kosmic was the beneficiary of some significant luck. Basically, every time Donkey Kong throws a barrel, there is a 1 in 32 chance that he will wait an extra half second or so before throwing the next barrel (this random process is explained in way too much detail in this Pastebin). Since the game’s bonus timer only ticks down when Donkey Kong actually throws a barrel, the semi-rare delay can give Mario the crucial extra frames he needs to reach the top of the kill screen using the broken ladder glitch.
Funnily enough, this randomized barrel-throwing delay can theoretically repeat indefinitely, provided the game’s randomizer picks the same lucky 1-in-32 sequence over and over again. If Donkey Kong decides to delay his barrel throw about 19 times in a row, Mario would actually be able to complete the kill screen normally, without the broken ladder glitch (and without facing many barrels, even). Of course, the chances of that happening on unmodified arcade hardware are nearly 1 in 40 octillion (1 in 32^19, to be precise), so don’t count on encountering it in the wild any time soon.
With the ladder glitch, though, Kosmic’s emulator-assisted run needed significantly less luck to pass the kill screen at 22-1. He was even able to push the game past the next four stages (including previously unseen spring and pie factory screens) to reach level 22-6.
Kosmic calls that stage the game’s true kill screen, as there’s currently no known way for Mario to remove all eight rivets quickly enough to overcome the glitch-shortened timer, even with emulator assistance. Then again, for decades, players assumed there was no way to complete level 22-1, either. Maybe someone will figure out a clever method for beating this new kill screen with 40 more years of sustained effort.