Mewtwo is a legendary Pokémon that was introduced in Generation 1 (Pokémon Red, Blue, and Yellow). While it appears in later generations, it's not available in Pokémon HeartGold.
How to get Mewtwo in other games:
* Pokémon Red, Blue, and Yellow: You can find Mewtwo in the Cerulean Cave after beating the Elite Four.
* Pokémon Gold, Silver, and Crystal: Mewtwo can be obtained through events and in certain versions of the game.
* Other games: Mewtwo can be obtained through various means depending on the game, including events, trading, and specific in-game methods.
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