>>52335292Mewtwo is classified as an urban legend in the Pokedex book.
In Gen 1, the Pokemon considered legendary were:
>the legendary birds>the Dratini line>Arcanine>Mewtwo>“Many Pokémon appear in the worlds of myths and legends. The most famous must be ‘The Phoenix.’ Previously, there had been few believing in the existence of such Legendary Pokémon. Since the discovery of Dratini, however, the non-believers are dwindling. Now, an endless stream of researchers embarks on expeditions convinced that the legends live.”>#147 Dratini: Legendary Pokémon live! A Safari Zone visitor just happened to catch a Dratini in the park’s pond. The lucky angler became an overnight sensation with news of the discovery exploding globally. This fortuitous accident convinced many that all legendary Pokémon exist without any doubt. It ignited a massive wave of Pokémon expeditions.">#150 Mewtwo: There is an urban legend of a mad scientist whose tenacious recombination of Pokémon DNA resulted in a horrifically brutal creature. Could such a frightening Pokémon really exist?”Dratini was the first "legendary" Pokemon to ever be discovered, and its discovery is what caused people to start believing that the rest actually existed too.
But the definition of "legendary" changed in Gen 2, so the Dratini line and Arcanine had their legendary status revoked.