As predicted several times, the third Detective Pikachu Case File will indeed feature Mewtwo-GX!
The case file includes a promo card, a coin, two Detective Pikachu booster packs, one regular booster pack, and a PTCGO code card.
Mewtwo-GX joins Greninja-GX and Charizard-GX as the three “case files” releasing for the Detective Pikachu TCG product line.
The Detective Pikachu mini-set will release through this and other Detective Pikachu promo products starting April 5th in the U.S. and March 29th in some international countries. Each booster pack will contain four cards; each card in the set is holographic.