This coding error occurred in World 1 level 2, which was introduced on screen as “World 1-2”. After Mario had glided through the wall and down the pipe in World 1-2, text would appear on the screen to indicate which new world and level he was entering, as per usual. But thanks to the glitch, there was a blank space where the world number would usually be, so it read as “World -1”. This secret level therefore became known as the “Minus World”.
Rumours of the phenomenon spread through word of mouth soon after the game’s release, before entering gaming folklore in 1988 when American magazine Nintendo Power reported on it. “Explore the mysterious minus world,” said the article, teaching readers how to access the hidden level. It’s now regularly celebrated as “the greatest glitch of all time”, but upon its discovery many questions arose: did Nintendo put the level there deliberately? Were there other secret levels in Super Mario Bros? Were there other secrets hidden in other games?
Nintendo’s legendary auteur Shigeru Miyamoto denied that the Minus World was a deliberate feature of the game. But it added to Super Mario Bros’s allure of unpredictability: here was a game whose gradually unfurling world was unlike anything that came before it.
“I remember finding [Super Mario Bros] kind of mind-blowing,” says author and video games scholar Dr Brendan Keogh, who recalls playing it for the first time at a friend’s house after school. “At that point, most of the games I was playing didn’t have backgrounds, they were just black. So seeing Mario Brothers, where it’s this very coherent world with fantastical creatures and fields and trees and bushes and clouds… It felt kind of limitless, in terms of what could be hidden that you haven’t seen yet.”
Some of the game’s other “secrets” were put there deliberately. Punch through a ceiling, for example, and you might be able to jump on top and walk past an entire level. But then there was this one big, accidental surprise. Nobody is sure who first discovered the Minus World, but it could only ever have been by mistake.