Mewtwo - The Prologue To Its Awakening
The episode, called Mewtwo - The Prologue To Its Awakening - (ミュウツー‐覚醒への序章‐ Mewtwo ~Kakusei e no Prologue~ Anime Special) is a two-hours anime special about Mewtwo aired in Japan July 11, 2013.
The story starts before Ash meet Mewtwo in the 16th movie.
Virgil, the Unova League Chapion, with his Resque squad go to a certain mountain and here he discover that an old man (Oscar) and a girl (Anna) meet a strange Pokémon: Mewtwo.
Then, they are approached by Danku, a man who tell to the group that he was rescued by Mewtwo. The Pokémon seems that has helped many Pokémon in the area but had also suffered a significant injury.
Virgil decides to heading to rescue Mewtwo with the help of his team of Eeveelutions and some wild Pokémon but Mewtwo seems that don't trust humans.
However Danku reveals his ambition to catch Mewtwo and the battle versus Mega Mewtwo starts.