There is a distinction between ROM hacks and 'bootleg games'. Though the core-series is by far the most popular series to hack, there are also many fan-created Pokémon games that do not use these as basis, and instead are, for example, modified versions of the Pokémon Mystery Dungeon series and Pokémon Conquest. These factors, as well as Pokémon’s notable popularity throughout the world, has lead to the creation of thousands of different games spanning multiple generations, ranging from minor adjustments to additional new features and, more and more frequently, entirely new fan-made Pokémon games.

The core series Pokémon game system is considered very versatile and lends itself well to modification, giving hackers a lot of creative freedom together with a solid, well-tested game engine.

The hackers achieve this by changing the code of the Read- Only Memory of a published video game to create something new. ROM hacks, also known as hack games or ROM patches, are video games that have been edited or altered by enthusiasts.

A warning to users about bootleggers included in Pokémon rijonAdventures

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