In 1988 the Famicom (or 'NES' as it was known outside Japan) had sold a little over 25 million units. This was due in no small part to its flagship game Super Mario Bros. Check out our own book all about the NES/Famicom, here.
Every good gamer knows that this wasn't the first title to feature Mario. Still, as it was released in North America along with the NES, it's how most gamers of that era came to know our friendly Italian plumber.
As this was long before the modern internet, players kept up to date with the latest titles, reviews and cheat codes through reading popular magazines like Nintendo Power.
Anyone who thumbed through to page 56 of the December '88 issue of the magazine would have seen a very peculiar entry in the "Classified Information" section headed:
"Explore the mysterious minus world".
Contributor "Agent 826" provided step by step instructions on how to get there. It involves standing Mario on the very last pipe in World 1-2. Players then have to master the tricky manoeuvre of jumping backwards through the wall. Those able to successfully phase through will come to a warp room, the outer two pipes of which will take them to World -1.
Enter the Minus-verse
For Western players using NES cartridges, the title screen shows "World -1" before Mario is transported to an underwater level, which repeats in an endless loop.
The disk-based Japanese Famicom version transports the player to a different "Minus World" altogether, where Mario floats on thin air, exactly as if he's underwater. This stage can be completed to progress to World -2, then -3 and so on. The Japanese version of Super Mario Bros. contained no fewer than 256 of these enigmatic hidden levels.
The first 'minus' secret level was printed in issue # 3 of Nintendo Power magazine in 1988. It sparked a quest by players to discover more secret levels. Source: Internet Archive
The Minus Mystery
In a 2010 interview with Famitsu magazine, Super Mario Bros. creator Shigeru Miyamoto was asked about these mysterious minus levels. He replied:
"That's a bug, yes, but it's not like it crashes the game, so it's really kind of a feature, too!"
He also said that these levels weren't deliberately placed there for fans to find. Still, it sparked the imaginations of players. If 'Agent 826' had been able to discover this secret level via a glitch, could there be other secret levels out there just waiting to be unearthed?
By the time the December 1988 issue of Nintendo Power had been released revealing the Minus level/s of Super Mario Bros., Super Mario Bros. 3 had just appeared on shelves in Japan.
Like its predecessors, it contained some well-placed secret areas and warp rooms but there were also some levels that officially didn't exist. That is to say they were there in the game's code but there was no way for someone playing the game ordinarily to access them.
In North American versions of Super Mario Bros. the 'minus' level is just a clone of World 7-2. But going through the pipe at the end just returns to the start of the level.
To date fifteen of these levels have been documented by players eager to scour the game's source code. Many are glitchy and unfinished but some can be played through.
Clearly not all these levels were there accidentally. The 1993 SNES game Super Mario All Stars even includes a remake of Super Mario Bros. 3 complete with these mysterious minus levels.
Charting the Minus World
Sharp-eyed readers will already have noticed the paradox facing players determined to explore hidden levels like the minus worlds. How can you go somewhere you can't locate? Even if you do know where it is, how do you get in if there's no entrance?
The 'debug room' in Final Fantasy VII was meant for developers only. It's filled with links to test game content like FMVs, towns and battle mechanics. Source: Final Fantasy Wiki.
While the very first "minus world" in Super Mario Bros. was probably discovered by chance, in the late 80's the fastest way to discover hidden secrets in code was through a technique known as 'ROM Dumping'.
This involved using a specialised device (such as the official "Famicom Disk System") to make a copy of the game's code to a disk or computer, from where the code can be examined.
The Famicom Disk System could also write to media and to this day there are unofficial disks of the Famicom Super Mario Bros. with modified code which allow players to access all 256 'minus' worlds hidden in the original version of the game.
One of the 15 documented levels which can only be accessed by hacking Super Mario 3's source code. This giant mystery block contains a rare 'tanooki' suit.
The Tennis Trick
Using specialist equipment to chart the minus-verse was feasible but expensive. It also required enough programming knowledge to tell the game to stop executing its code in the normal way and jump straight to the hidden levels.
Gamers without access to ROM dumping and code editors tried putting in cartridges at different angles and even breaking out soldering irons. Eventually Family Computer Magazine came to the rescue with a workaround that uses both a Super Mario Bros. cartridge and one for the 1984 NES game Tennis.
Nimble fingered players would fire up with the NES with the Mario game inserted. They'd then quickly switch cartridges to Tennis and reset the console. They'd play Tennis briefly, tossing the ball twice, serving, walk their character around, then quickly switch cartridges again.
YouTuber Sharopolis uses a Famicom to discuss the Mario/Tennis glitch in detail. The games share certain memory addresses, so swapping carts in a specific way allows players to access the Minus Levels.
If the gamer then reset the console holding A + Start, they'd start in a new Mario world - the level depends on the number of steps taken whilst playing Tennis. As the first 'minus' world officially counts as world no. 36, it and others can be accessed in this way.
For players unable to play this cartridge hand jive, inexpensive cheating devices like the Game Genie and Action Replay could modify the game's source code to jump to hidden levels using special codes.
The 'Hidden Palace' Zone was removed from Sonic 2 due to memory limitations but was later finished and restored for the 2013 remake. You can also play the original unfinished 'Proto Palace' level (pictured) via a cheat code.
The Minus Legacy
It's very easy to dismiss 'minus' or 'hidden' levels as junk data. In some cases they're removed from the game for a good reason as they're too difficult or unfinished. In other cases, such hidden areas may exist for the benefit of game creators, such as the "Debug Room" in Final Fantasy VII.
Part of the intrigue of these hidden levels is that game creators are notoriously cagy about them. For instance, for years the mysterious secret multiplayer "Citadel" level in GoldenEye existed only as a name in a couple of memory addresses in the game's code.
It wasn't until 2004 that skilled programmers found the necessary 'Gameshark' codes to load the background and textures of the level itself. This was done despite claims by developer Rare that Citadel wasn't in the final game in any shape or form.
YouTuber Nathan Spielman walks viewers through the unfinished 'Citadel' map in Goldeneye for the N64 using a GameShark Pro.
Other game creators are more candid. The "Hidden Palace Zone", which was originally removed from Sonic the Hedgehog 2 for Mega Drive was later restored in the 2013 mobile version of the game.
If you're intrigued by lost levels lurking in the code, don't forget to explore the untold mysteries and gripping tales of those titles that never saw the light of day in The Games that Weren't which is currently reprinting and due in August.