MUGEN fighting games’ strongest characters can break a computer

While most “who would win” battles take place in the unfettered realm of the imagination, in 1999 a group of anonymous software developers released a little program called MUGEN that lets you make them a little more real.

MUGEN appears to be one of the zillions lousy companies. Street Fighter 2The 1990s saw a lot of ripoffs. When you open the game, however, it only features one character — a nondescript martial arts artist called Kung Fu Man. That’s because MUGEN isn’t exactly a game — it’s a construction kit for fighting games, assembling tools to create characters from the ground up. It’s amazing how many people have made characters.

You can download a few files to have Peter Griffin and Jake face-off AvatarJake, or? Adventure TimeJake, from State Farm. There are tens of thousands of MUGEN characters, covering every franchise. Are you familiar with all of the Power Rangers characters? Sure. Yes. You are correct. Caillou? Caillou comes in about eight versions.

All pop culture is subject to the same eternal question: “Who would win?” Here are the answers. Get ready for Polygon’s Who Would Win Week.

You know when you’re arguing “who would win” there’s always someone who tries to bend the rules to get the outcome they want? MUGEN lets these individuals shine and allows them to become more powerful characters who can take down your Kung Fu Man every day without getting a sweaty. The community has a name for these creations: “cheapies.”

It’s pretty easy to make a strong character in a fighting game. Allow them to use powerful and fast attacks that can reach far reaches. There are many MUGEN characters who fit this description. A Ronald McDonald edit named “Dark Donald” is one of the most notorious, as is the dreaded “Omega Tom Hanks,” who can fill the screen with damaging DVDs of the actor’s famous films. A cheapie is a completely different story. You’re not meant to be able to play against them at all, let alone win.

The first shot was fired by a character designer who goes by “Ironcommando” with the release of “A-Bomb” in 2008. This character is about as simple as you can get — just a static image of a cartoon bomb, apparently drawn in MS Paint. Pressing any attack button or getting hit by anything triggers his sole offensive move — a massive, screen-filling explosion that cannot be blocked and kills any foe.

It would be a great play to win the title of most powerful fighter in fighting games. However, the Cheapie Warfare was just beginning and would continue to get absurder.

What can you do to beat this? It wasn’t long until character creators found a way. MUGEN supports “reversal” moves — commands that, if they are timed correctly, negate the opponent’s move and counter them with an attack of their own. So a reversal character would simply trigger A-Bomb’s explosion, reverse it automatically, and win.

One of the next entrants in the nascent Cheapie Wars was “F1,” named after the key that, when pressed in MUGEN’s debug mode, instantly killed the fighter on the second-player side. When the round began, F1’s artificial intelligence would have it access the console and execute that command, immediately winning the fight without having to worry about reversals. Other creators discovered ways to stop the F1 key being recognised, eliminating that vulnerability.

MUGEN is different from other character-creation games because there are very few guardrails. When you create a wrestler in a WWE 2K game, you can’t make them 50 feet tall and able to crush the entire ring under their boots. The result? Dark Souls adventurer isn’t going to be so buff that the game bows before them. But MUGEN doesn’t restrict creativity in order to preserve a sense of balance. That has lead to wild choices in the race for the most powerful character.

Cheapie makers would quickly discover new methods and use them to destroy the most powerful characters, thereby establishing themselves as the top of the mountain. These coding techniques and hacks were used to divide cheapies into “tiers.” The starter tier was named “nuke” after A-Bomb — characters that don’t do anything outside of the game’s basic ruleset to instantly deplete their opponent’s life.

K. Thor Jensen is the Polygon photographer.

Soon afterward came the “null tier” cheapies, which were the first to exploit MUGEN’s code itself. Character creators discovered a bug that allowed for character code to access variables and properties outside of itself by overflowing a buffer with blank “null” controllers. By targeting a specific overflow point, these cheapies could simply switch the opponent’s “alive” property to “false,” killing them immediately and ending the round.

A cheapie fight is lost the instant it begins because they do not use the core interactions of MUGEN. These fights take place in the fraction of a second in between “Round 1 — fight” and “KO.” To create new and more powerful cheapies, designers had to find methods that would deploy before their opponent’s. To find better and faster exploits, hackers went deep into how MUGEN packed and loaded characters.

Some extreme ideas were born out of the Wild West nature this process is. A cheapie category called “secretary tier” involved the character hiding a prog.exe file in a temp folder to manipulate the data coming into and out of MUGEN. “Postman tier” cheapies do something similar, but with a .bat file. Some of these characters not only win rounds but also use custom code overwrite their opponent’s data and make them instant die. FutureFighting.

Cheapie construction methods are becoming more common. “Omed tier.” “Whale tier.” “Hypernull tier.” The wars waged fast and furious over MUGEN fan forums, with some even instituting new rules to block the sharing of particularly nefarious characters.

This is where it all ends. In theory, with the introduction of “dragon-tier cheapies,” which allegedly use MUGEN to not only run external code but actual malware, causing the computer they are run on to brick itself and become unusable. That’s a pretty definitive win condition, and it’s hard to imagine any character that could top it.

So I decided to try these powerful PC-destroying heroes out myself. I got an old laptop, installed MUGEN and then took it apart. Then I dug through forums and archives to download as many cheapies as I could find, with bizarre names like “END_White-Day” and “Undefined Universe.” Once I had a roster built up, I set up a tournament of champions from as many different tiers as I could find.

The experience was fascinating, but also nerve-racking. I couldn’t get my hands on any dragon-tier cheapies, and some in the community claim they don’t exist. Most web hosts don’t like downloading malware-infected files. I was able to get cheapies from many of the other tiers — postman, null, secretary — and these fighters did a number on both MUGEN and each other when I had them play matches. Rounds were over before they began, and sometimes extended into infinity. The combo counters increased to the triple digits while neither of my competitors fell. Displays and menus crashed, program locks were repeatedly triggered, and the entire tournament fell apart in a blaze of nightmare code.

Windows 2023 has fixed the majority of vulnerabilities that caused the Cheapie War to grow to such an extent. MUGEN, however, is still in widespread use and hackers have found new, more sophisticated ways to hack it. So maybe the next cheapie will be Skynet itself, able to gain sentience and finally settle the “who would win” question once and for all.