From Bulbapedia, the community-driven Pokémon encyclopedia.
New Island is the island where Mewtwo was created in the story arc of the Pokémon anime (in the game he was created on Cinnibar Island). At the beginning of Mewtwo Strikes Back, Mewtwo woke up in a tank after slowly maturing for many years. He started out being curious about what he was here for. After a short conversation with them, however, he soon saw that the scientists saw him more as the end result of their experiement and less as a living thing. The scientists paid for this coldness with their lives when Mewtwo destroyed the lab completely. After having been used by Team Rocket as a tool for evil, Mewtwo returned to the island and rebuilt the lab as his lair. However at the end of the movie, the island was abandoned once again.