New episode title(s) has/have been added to the database. Title: ポケモン映画が１００倍楽しめるアニメ「ミュウツー　～覚醒への序章～」/Pokémon eiga ga 100-bai tanoshimeru anime 'Mewtwo ~ kakusei e no prologue ~'. Please comment below! Thanks, your friendly PM.Net AnimeBot

A special episode as a prequel to a movie? That is quite unusual. I wasn't really sure what to expect from this one. But it turned to be surprisingly good for just a prequel.
We actually got the Team Eevee rescue squad (the winners of the league) as the main heroes. That was quite surprising.
And also a little girl who obviously has supernatural powers, allowing her to talk to call forest Pokemon at her aid.
But we see how powerful he is, especially in the new forme, despite his injuries.

Also, we get to know another Pokemon Hunter.
Only a shadow of Mewtwo's background story is mentioned in this prequel though. I hope more info will be given in the movie itself. So far it only became a bit confusing as it is not the same Mewtwo as the one from the 1st movie.

The animation quality of this prequel is somewhere between a normal episode and a movie, being much more close to the movie-like animation.

My rating:
For a special "episode", which was probably meant to be just part of the advertising for the new movie, it was very good and surpassed expectations and brought an interesting cameo of Virgil and his Eeveelutions.
I give it 10