The official Pokémon movie website has updated. Translations follow:
You'll Get an Ancient Mew Card Via the "Mewtwo Strikes Back Evolution" Theater Pamphlet!!
A "Mew" Pokémon card with its text written in ancient letters is included as a free gift
with the theater pamphlet for "Mewtwo Strikes Back Evolution", which premieres Friday July 12th!
The back of the ancient Mew card has a different design from the normal cards.
The pamphlet goes on sale alongside the movie's premiere on Friday July 12th!
Details on the theater pamphlet will be revealed at a later date. Stay tuned!
The way to decipher the letters written on the card
is scheduled to be revealed on the
Trainers' Website, the official Pokémon Card Game website,
on Friday May 24th, the same day we present the cards included in the expansion pack "Miracle Twins".
Source:
https://www.pokemon-movie.jp/news/?p=3638