From Bulbapedia, the community-driven Pokémon encyclopedia.
Pokémon Purple is a hack of Pokémon Ruby version that the story continues in Hoenn, with the player's starting area being Littleroot Town. While the games feature several expansions in key areas, the overall plot follows the same direction as the original Pokémon Ruby and Sapphire, with Team Magma capturing the legendary Darkrai. Some wild battle aspects exclusive to Ruby and Sapphire are also included, such as the battle with a Mewtwo wearing an armor similar to that from the Pokémon anime.
Purple features some of the 4th generation Pokémon included such as Shinx and Buizel, as well as the Ho-Oh event with the use of the Aura Ticket (which is actually an Eon Ticket). It also features 5th generation Pokémon such as Victini and Snivy.
The Mew event will be also triggered with the Mystery Orb (which is the Blue Orb changed), which is accessed through a Gameshark code. XD001 from Pokémon XD: Gale of Darkness will make another appearance, along with the new Shadow Pokémon such as Articuno, Zapdos and Moltres. Changes includes some Pokémon changes colors and types, changing move names such as changing Psycho Boost to Psy Blast, new areas such as Darkside Cave, Metreon Cave and Metreon Way, generations IV and V Pokémon, and such. This game was created by TheShinyMew with the use of the Pokémon Ruby engine. However, it is unknown it has been sold in the cartridge, just the ROM itself.