>>54556207He invented the ubers tier. He was more broken in his initial generation than any pokemon has been in their respective game since. In RBY you do not "counter" mewtwo, you do not "check" mewtwo. You use another Mewtwo, or you lose. He buck broke gamefreak so hard they paniced and made 2 more types just to attempt to slow him down. His movie packed the theaters. He made it into Smash Bros before charizard himself. His BST set the benchmark for all cover legendaries to come.
Other pokemon may be superficially rare, but Mewtwo is one of the few that truly represents the title "Legendary"