Due to the popularity of Pokémon in the late 90's and early 2000's, many pirated hacks, mainly on the Famicom/NES and Game Boy systems, were made out of already existing games by replacing aspects of them to be centered around Pokémon. The majority of them barely change any aspects from the original games they were trying to pass off as real Pokémon titles.
"Colored" NES hacks
A series of Famicom/NES hacks named after different colors, similar to the original Game Boy Pokémon titles. Due to suitable graphics of the characters not existing at this point, the majority of graphics are poorly drawn and incorrectly colored.
- Main article: Pokémon Golden
A hack of Tom and Jerry that replaces some of Jerry's graphics with Eevee; a considerable amount of the original graphics remaining intact. The title screen reads "GOLDEN" and the copyright screens and story were removed.
A hack of Tiny Toon Adventures where some of Buster Bunny's graphics are replaced with a very poorly drawn Pikachu. The turning sprite after running fast is a garbled Mario sprite, likely from Super Bros. 6. The title screen features a large Pikachu with no actual title, and the original story was removed.
- Main article: Pokémon Green (Famicom)
A hack of Kero Kero Keroppi no Daibouken 2 that replaced Keroppi with a green Clefairy, and changed his musical attacks to generic bullets. The title screen reads "GREEN" and the copyright screens and story were once again removed.
Another Kero Kero Keroppi 2 hack, this time featuring Suicune. The changes made in Pokemon Green also apply to this hack. The title screen and character sprites are exactly the same as the hack "Monsters" (seen below).
A hack of Wacky Races that replaces Muttley's graphics with Blastoise. Unlike the other hacks, the story is intact and unedited. Funnily enough this game is sometimes called "Blue Cat" on multicarts, likely from a misinterpretation of the title screen graphic.
A hack of Mitsume ga Tōru that replaces some of Hosuke Sharaku's graphics with Charmeleon. The game starts on level 2 and removes the story. It is also known as "Pokemon 2000" on some releases (not to be confused with the Y2K hacks).
A hack of Little Nemo: The Dream Master that replaces some of Nemo's sprites with a silver Sandshrew. All of Nemo's transformation graphics were left intact.
A hack of Magical Doropie (AKA The Krion Conquest) that replaces Francesca with Suicune. The actual "colored" name of the game is unknown, and the title screen simply reads "MONSTERS".
"Y2K" NES hacks
Basic hacks intended for release on Y2K-branded multicarts.
- Main article: Pokemon (Y2K)
A hack of Nuts & Milk that replaces the characters with Pikachus,and removes the title screen logo.
A hack of Warpman that replaces the main character with Pikachu, and removes the title screen logo.
Pokemon 2000 / Pikachu Y2K
Two nearly-identical hacks of Felix the Cat which replace Felix with Pikachu. Pokemon 2000 features a gray Pikachu, while Pikachu Y2K corrects him to yellow. Both versions also feature different title screens, and are often called "Pokemon Yellow" on the cartridge label. Interestingly, this is the only known Y2K game to receive a single-cart release, as the others exclusively appear on multicarts.
Yet another Felix the Cat hack, based on the coding of the prior two. This hack replaces some of Felix's transformations with Charmander, while some others are still Pikachu. The game has only been found as a built-in game on one Famiclone called the PS-Kid. It appears on the back of the box for multiple systems (such as the Super Video Game), but doesn't actually appear on any of them.
Hacks, mainly made by Inventor, featuring Pokemon characters, originally released on various plug 'n plays.
Also know as Pka Chu, Pika, Pika Man and Pocket World is this hack of Super Mario Bros. featuring Pikachu (with his small form being an anthropomorphic Pokeball). It uses the same music as Pandamar, another hack of SMB by Inventor.
Barve Boy - Kung Fu Pokechu
A hack of Jackie Chan that replaces Jackie Chan with Pikachu. The opening intro also features a girl Pikachu and Mewtwo. The music is completely muted during gameplay.
A hack of Nekketsu Kakutou Densetsu that replaces all of the characters with Pikachu lookalikes. The game is also fully translated into English, albeit poorly. The music cues are swapped around, and the copyright screen is replaced with Pikachu laughing.
A hack of Chip 'n Dale Rescue Rangers 2 that replaces Chip with Charmander (erroneously named Pika) and Dale with Po (from Teletubbies). The first boss is replaced with another Charmander, and Pikachu and Mario appear in the cutscenes. The dialogue is poorly translated in a rather humorous way.
- Main article: Pokemon 2
A hack of Adventure Island 3 that replaces Master Higgins and his girlfriend with Pikachus, and changes one of the items into Staryu. The game starts with two of each item unlocked in the inventory. The title is stylized as "ミュウツーの Pokemon II - 2" (Mewtwo's Pokemon II).
Game Boy hacks
Hacks released for the Game Boy or Game Boy Color systems. Despite being the system commonly associated with Pokémon at the time, there are very few compared to the NES hacks.
Monster Go! Go! Go!!
- Main article: Monster Go! Go! Go!!
An advanced hack of The Smurfs 3 that replaces the playable Smurf with Pikachu, changes enemies to various other Pokémon, and converts the game to color (the original was in monochrome). The hack suffers from extreme slowdown, running consistently at about half speed.
Pokemon Action Chapter
A hack of Smurfs Nightmare, an official Game Boy Color conversion of The Smurfs 3 that released after Monster Go! Go! Go!! did. It only replaces the title screen and Pikachu sprite, leaving everything else intact.
Monster Go! Go! II
The sequel to Monster Go! Go! Go!!; it is a hack of Kirby's Dream Land 2 that replaces Kirby with Pikachu the enemies with various pokémon, and converts the game to color. All other elements remain intact.
Pokemon Diamond and Jade
- Main article: Pokémon Diamond and Jade
Bootlegged versions of Keitai Denjuu Telefang 1. The Power version was used to make Diamond, and the Speed version was used to make Jade. These games have numerous glitches and translation errors that weren't present in the original game. English and Chinese versions were also produced for both games.