Edition: The earliest editions of the Mewtwo promo card, such as the one released in 1999 as part of the Japanese "Pokémon the Movie 2000" promotion, are generally more valuable than later reprints.
Condition: The overall condition of the card, including factors like surface wear, creases, bends, and ink marks, significantly impact its value. Cards in mint or near-mint condition are typically worth more.
Language: Mewtwo promo cards released in different languages can have varying values. For instance, English-language cards are often more sought after and valuable compared to cards printed in other languages.
Rarity: The rarity symbol on the card, such as a star or holofoil pattern, can indicate its scarcity. Rarer cards are generally worth more.
Based on these factors, the value of a promo Mewtwo card can range from a few dollars for a common, non-holofoil reprint in good condition to several hundred or even thousands of dollars for a rare, holofoil edition in mint condition. It's important to note that the value can fluctuate over time based on market demand, availability, and other factors.