A mapper hack is a game ported from one board (that is stored inside the cartridge and that contains all the game's data and (sometimes) tiles) to another, more simple and easier to reproduce. This feature is somewhat well-known among the romhacking community, although, in order to save spendings, pirates also exploit this feature. In certain cases, this results in the final result being drastically butchered compared to the original. Mapper hacks are also often made to work on new bootleg reproduction cartridges or multicarts. In the case of official games, these are usually converted from MMC1 to MMC3 because the former mapper doesn't work on most multicarts.
Sometimes, dumpers use this technique in order to make bootleg games with complicated mappers work on most emulators. The most well-known example of post-dumping hacking is Kart Fighter.
Examples 
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- Super Lion King has two versions available. The original one shows the Super Game logo for a longer time and has Bug Toss minigame. The mapper hack, despite maintaining most of the game's data in safety, removes this minigame, although leaving the pickupable bonus item available.
- The mapper hack of Aladdin by Super Game has four levels available, as well as several constant graphical glitches. The full version has been discovered recently, with most of the levels from the original game available, as well as the actual intermission graphics from there, contrary to these ripped from the Sega Mega Drive version of Prince of Persia.
- Aladdin by Hummer Team is also known to have at least two MMC3 hacks. The more commonly distributed one lacks in-game music and background animations whereas the other one includes these.
- Ture MK3 has one known as Mortal Kombat 4. Contrary to the fact that mapper 4 board can actually hold 256K CHR-ROMs, Mortal Kombat 4 automatically cuts half of the graphics present in the original version, which results in having a regular 128K CHR-ROM. (The original game was 384K, having an extra 128K of graphics) In the mapper hack, there are only four unique fighters and three stages, yet most of the music is buried inside the game's data. The removed characters are still present by name, but are essentially the four characters retained in this version.
- Samurai Shodown by Rex Soft has one named Samurai Shodown III. In order to look more like its original version, it duplicates the roster not twice, like before, but thrice.
- Street Fighter Zero 2 '97 already had two sets of repeating fighters originally, but (because MMC3 can't have 512k CHR-ROM) the mapper hack leaves only four original fighters intact, plus no intro cutscene. Unlike this game, The King of Fighters '96 has already been ripped, mainly because Ka Sheng never produced cartridges with memory bigger than 512K.
- Street Fighter II Pro by Cony Soft has several mapper hacks available. One of them is Street Fighter V, which duplicates the cast, yet removes Sagat and M Bison/Vega from the roster, and replaces Ryu's icon with Goku's. Another one, included on multicarts quite frequently is Street Fighter VI which uses even more simplified graphics for main menu and removes Dhalsim and Zangief. Both of them use only two unique stages, which use different palettes depending on whom the player is fighting.
- Mortal Kombat II has one, which duplicates all of the fighters in the roster, but keeps the content intact. Another one, included on 10000000-in-1 multicart, is possibly 256K big, compared to the original (which was 384K). Despite this hack having every fighter from the original, the stages were drastically simplified.
- Boogerman has no sound on Super 303 3-in-1 multicart, which may provoke a guess that this multicart have used the mapper hack of this game.
- On multicarts, Tengen Tetris, TwinBee, and Arkanoid are commonly included in NROM format as opposed to the original mappers they used. (TwinBee used a Konami mapper and Arkanoid used CNROM while Tetris used a custom Tengen mapper which functions the same as CNROM) This results in the games having fewer graphics than the original versions, causing graphical glitches in the latter two. Tetris has its title screen and high score screen removed to prevent this.
- Spider-Man: Return of the Sinister Six has a mapper hack version of it, which reduces the size of the game from 384K to 256K, removing most of the cutscene graphics in the process. This version is sometimes included on multicarts. Oddly, some versions of this hack retain the copyright while others don't.
