It'd be remiss not to include the glitch that pretty much kicked off gamers' eternal hunt for secret levels in Mario games. This level above, eerily labelled '-1', Negative World or Minus World isn't actually supposed to exist, and restarts when you reach the pipe at the end, keeping Mario forever stuck in a lethal watery loop. How to unlock it: At the end of World 1-2, instead of exiting through the green pipe, jump on top of it, face left, crouch, then jump backwards to the right until Mario glitch-slides through the pipe and gets carried over to the warp zone. Jump into the first pipe to enter World -1. If you happen to own a Japanese NES, then the minus world is way more psychedelic, featuring three levels of strangely-coloured worlds, grey Bowsers, and a floating princess (foreshadowing her hovering abilities in Mario Bros. 2, perhaps?).
Gamer, Researcher of strange things.
I'm a writer-editor hybrid whose writings on video games, technology and movies can be found across the internet. I've even ventured into the realm of current affairs on occasion but, unable to face reality, have retreated into expatiating on things on screens instead.
