If I recall correctly, I thought Mew / Mewtwo was the strongest Pokemon of all time. I saw the movie, and the story about Mew being the original one, and being so powerful. I also heard that Mew was stronger than Mewtwo from a PokeDex entry, or something (which was obviously false after I got into competitive). Team Rocket members were discussing about how Mewtwo was the strongest Pokemon ever during the movie, and that led me to believe that Mew or Mewtwo was the strongest Pokemon of all time. Their battle style was quite powerful, and none of the regular trainers could even get a scratch onto Mewtwo. But yeah, I totally judged everything upon what I saw in the anime. xD;