Gaming · 5 min read

How Mortal Kombat's Blood Code Created the ESRB

Jeziel Fonseca·July 30, 2026

A dramatic 1990s arcade cabinet bathed in crimson and amber light inside a darkened arcade, glowing joystick and buttons casting a red hue on a wet floor, moody cinematic atmosphere

On September 13, 1993, what the gaming industry called "Mortal Monday" quietly became one of the most consequential days in the medium's history. The same game shipped on two competing consoles simultaneously. One version had grey sweat instead of blood. The other had a seven-button cheat code hidden on the options screen. The difference between those two versions eventually produced every age rating label you see on a game box today.

Two Versions of the Same Day

Mortal Kombat landed on SNES and Sega Genesis on the exact same day as part of a coordinated multi-platform launch. The arcade original was a gory fighting game built on digitized actors and finishing moves (called Fatalities) that involved spines, heads, and a fair amount of blood. Both console ports arrived with that reputation fully intact in the minds of players.

Nintendo had other ideas. The SNES release went through Nintendo's content approval process, which at the time applied strict standards to any game released on the platform. The result: all blood was recolored grey and described in-game as sweat. Fatalities were altered or removed entirely. Sub-Zero's spine-rip became a freeze-then-shatter. The game was, by arcade standards, defanged.

The Genesis version went through no such filter. Sega allowed a content code instead, and developer Acclaim hid it on the "Code of Honour" screen before the main menu: A, B, A, C, A, B, B.

The Code With Three Layers

The code itself was a deliberate piece of wordplay that almost nobody noticed in 1993.

The Sega console sold in North America was named the Sega Genesis. The British rock band Genesis released their eleventh studio album, "Abacab," in 1981 (the title came from labeling song sections A, B, and C, then arranging them: A-B-A-C-A-B). The blood code riffed on that album name with one extra B appended to make it seven characters: ABACABB.

Console name, band name, album title -- all folded into a single code. Guinness World Records later recognized ABACABB as the first cheat code ever used to uncensor a video game.

What the Sales Numbers Said

The two versions launched at the same time, at the same price, to the same market. Players had a direct choice between them. The result was not close.

Multiple sources, including SYFY Wire and contemporary gaming publications, put the Genesis version outselling the SNES version by roughly five to one. The uncensored version was simply what players wanted, and the market made that preference unambiguous.

The problem was that this was 1993. Games were selling at a scale that attracted political attention, and the content question was no longer purely commercial.

The Senate Hearings

On December 9, 1993, less than three months after Mortal Monday, US Senators Joe Lieberman (Connecticut) and Herb Kohl (Wisconsin) convened joint hearings of the Senate Subcommittees on Juvenile Justice and on Regulation and Government Information. The games called out by name included Mortal Kombat and Night Trap (a live-action horror game involving actresses being attacked). A second hearing followed on March 4, 1994.

The message from Lieberman was explicit: the industry could create its own rating system, or Congress would create one for it. This was not a threat made in passing. Lieberman had already drafted legislation.

The gaming industry read the room.

How the ESRB Got Built

The Entertainment Software Rating Board was established by the Interactive Digital Software Association (the predecessor to today's Entertainment Software Association) and launched officially on September 16, 1994, roughly nine months after the hearings. The board adopted the familiar rating categories still in use today: EC (Early Childhood), E (Everyone), T (Teen), M (Mature), and AO (Adults Only). Content descriptors appeared alongside ratings to explain specific reasons for the classification.

The system was voluntary rather than legally mandated, which was specifically what Lieberman's ultimatum had demanded. The industry self-regulated before Congress had to act.

What is easy to miss looking back is how close a mandatory federal rating system came to existing. Had Lieberman's legislation passed, the structure and values of game classification might look very different now. The ESRB exists in its current form because the industry moved first, and it moved first because Mortal Kombat's blood code proved that players wanted the uncensored version, and that information moved fast enough to attract congressional attention within a single news cycle.

The Lasting Shape of What Happened

Every M, T, or E rating on a game box today descends from a decision made by Acclaim and Sega in 1993 to hide the arcade-accurate content behind a seven-button sequence instead of simply removing it. That decision produced sales data that embarrassed a platform holder, attracted Senate scrutiny, and forced a voluntary rating system into existence within a year.

It is also worth noting what the ESRB did not stop. Mortal Kombat continued as a franchise, added a franchise's worth of increasingly detailed fatalities, and is still releasing mainline entries today. The rating system that the original game helped create has let players and parents make informed choices without banning content outright. That is genuinely what the design intended.

Understanding where game ratings come from changes how you read them. The letter in the corner of a box is not a neutral technical description. It is the inherited shape of a political negotiation that happened in a Senate hearing room in December 1993, touched off by a game that most people remember for its action but few remember for its aftershock.

For anyone building a record of the games they have played, knowing that history adds a layer of context to the library you are cataloguing. Every game you track at The EndWiki arrived with a rating that traces back to this exact moment. If you want to start building your own gaming history, create a free account and the log is yours.

The games that shaped gaming culture are worth knowing well. For a broader look at how the way we classify and discuss games has evolved, see our guide to the evolution of game review culture.