What subtitle followed Pokémon: The First Movie in its English title?

The subtitle in the English title Pokémon: The First Movie is “Mewtwo Strikes Back”.

The 1998 Japanese animated film is commonly known in full as Pokémon: The First Movie—Mewtwo Strikes Back. Its main feature follows Mewtwo, a genetically engineered Pokémon who challenges humans and Pokémon after questioning the circumstances of its creation.

The theatrical release was accompanied by the short film “Pikachu's Vacation”. Some extended home-video versions also included “The Uncut Story of Mewtwo's Origin”, a prologue about Mewtwo's early history.

The title is sometimes shortened to Mewtwo Strikes Back, but that phrase is the subtitle rather than the full English title. It should also not be confused with Pokémon: Mewtwo Returns, a later television special, or the 2019 computer-animated remake Pokémon: Mewtwo Strikes Back—Evolution.