Question: why mewtwo is in kalos?
Answer: The Unknown Dungeon (Japanese: ななしの洞窟 Nameless Cave) is a very small cave in southern Kalos that can be accessed from Pokémon Village. A sole Mewtwo resides in the center with a game-specific Mewtwonite. ... Its purpose as a place to catch Mewtwo is a direct reference to Cerulean Cave in Kanto.