ROM hacks, also known as hack games or even ROM stains , are video games that were edited or changed by fans.

The core string Pokémon game system is considered very versatile and lends itself well to adjustment, giving hackers a great deal of creative freedom together with a solid, well-tested engine. These factors, as well as Pokémon's notable popularity throughout the globe, has resulted in the creation of thousands of unique games spanning several generations, which range from minor adjustments to additional new attributes andmuch increasingly more frequently, entirely new fan-made Pokémon games. Although the core-series is undoubtedly the most popular series to hack on, in addition, there are numerous fan-created Pokémon games which don't use these as foundation, and instead are, by way of instance, altered versions of the Pokémon Mystery Dungeon collection and Pokémon Conquest.

There is a distinction between ROM hacks and"bootleg games". These are real copies of published games which are sold to customers, frequently flashed on multi-player sport paks or sport titles and lacking the official Nintendo Seal. However, as ROM hacks are usually distributed over the Internet at no cost, they are often marketed as bootleg games, normally against the hacker's wishes. The reliability of those bootlegs are often poor, and is now such a problem that hackers have begun to introduce warning screens into their games, cautioning users that if they paid for this, they might have been scammed.

These were frequently relatively minor adjustments like sprite or dialog changes, and could generally follow the flow of the game. These ancient ROM hacks were infamous for being especially crude in nature, which range from swapping Pokémon and individual sprites about to replacing the dialog with obscene text.

This trend continued until the launch of Pokémon Brown by consumer Koolboyman from the early 2000s, one of the very notable Pokémon hacks ever. This was the first hack to completely re-invent the match, using a brand new area and completely new storyline. Later variants included an enlarged Pokédex (like Pokémon in Generations II, III and IV), additional dungeons and additional plot tweaks. It's but one of the very few completed hack games pokemon sword rom and has been powerful enough to justify a sequel (Pokémon Prism, a Pokémon Crystal-based hack on ) and also a Generation III variant (Pokémon rijonAdventures) based on Pokémon FireRed.

Since Brown, Pokémon hacking notoriety has expanded exponentially, with developers creating many applications tools for desktop operating systems to help generate maps, edit sprites, images as well as creating scripting languages particularly for the Pokémon engine. In addition, it has inspired many hackers to learn to edit the games' assembly code directly (known as ASM hacking). Several hacks have been released, frequently with FireRed as a base, for example Pokémon ShinyGold, Pokémon Naranja and also the Pokémon Ruby Destiny show, simply to name a few.

There are lots of sites dedicated to Pokémon ROM hack development. Many of these websites hold award nominations and services to showcase some of their best gifts of the community.