Finally it's been revealed that the Character Gx Case File from the Detective Pikachu products will feature Mewtwo. Mewtwo-GX Case File will have one regular Booster Pack, two Detective Pikachu Booster Box, promo Mewtwo-GX, coin, and a PTCGO code card.
Detective Pikachu is just 3 weeks away, releasing on the 29th of March.
As soon as we get more information we will be sure to let you know.