Mew (M01)

Mew first appeared in the first ever feature-length movie, Mewtwo Strikes Back, or Mewtwo versus Mew.

In this movie, Mew made a couple cameo appearances at the start of the before any major ones. A Mewtwo was cloned from Mew's DNA, a tiny bone looking slightly like a feather. Later, Mew started appearing around New Island while Mewtwo was testing his starter Pokemon clones. Mew followed Team Rocket into the main part of the island so it could stop Mewtwo from technically destroying the world. When Mewtwo's other new clones appeared, Mew came with them, however, it did not actually reappear until just a bit later. When it did appear, it got into a battle with Mewtwo. It was actually, however, trying to stop it's cloned form the whole time and was apparently only fighting to keep Mewtwo from destroying it. After Ash was killed and revived, and Mewtwo flew away with all it's clones, Mew went with them. In about the last minute of the movie, Mew appeared to Ash, but Brock and Misty never saw it.