The Mewtwo Project was the name of a Team Rocket project in the Red, Blue, and Green arc of Pokémon Adventures. Its purpose was to artificially create the most powerful Pokémon ever by enhancing the DNA of Mew. Originally intending to just synthesize the DNA, it was discovered that there wasn't a sufficient amount. Blaine had to use cells from his own arm to complete Mewtwo, making them dependent upon each other, and causing Blaine to defect from Team Rocket after Mewtwo escaped. They did not get the Mew Disk. Most of the scientists involved in the project were killed when Mewtwo destroyed the Cinnabar Lab in And Mewtwo Too!?.
It is a floppy disk containing data relevant to Team Rocket's Mewtwo Project. Green stole the disk sometime prior to Tauros the Tyrant. When he infiltrated Team Rocket's ranks at the Celadon Game Corner, Red learned of its theft and decided to seek Green out, as she had also stolen his Badges in the previous round.
After finding Green, she and Red were attacked by Team Rocket, who had discovered their actions. Using her Ditto, Green managed to defeat the Team Rocket Grunts and trick them into taking an imitation of the Mew Disk.