Pokémon Diamond and Jade is a counterfeit of the game Keitai Denjū Telefang which was unofficially translated from Japanese to English. The Power Version was used to make Diamond, and the Speed Version became Jade. The name Pokemon Jade has also been used for another pirated game that used Sonic Adventures 7. Some cartridges contain both Diamond and Jade in one or come bundled with a pirated poorly translated Pokémon Crystal.
The creature on the box art of Pokémon Jade is not from either the Pokémon series or Keitai Denjū Telefang but is instead the forest spirit from Hayao Miyazaki's film Princess Mononoke. Many of the knock-off cartridges also contain serious programming errors which cause the game to crash.