The official Pokémon movie website has updated with a site-wide riddle system. Translations follow:
A Special Riddle Session Commemorating the Real Escape Game/Mewtwo Strikes Back Evolution Crossover "Escape From Mewtwo Castle"!
Try solving the riddles!
You are a Pokémon Trainer who has lost your way into Mewtwo's castle.
It appears you will have to discover hidden riddles and codes in order to escape.
Solve all the riddles and escape
before you're found by the Mewtwo Balls, which will try to steal your Pokémon!
The first clue!
Search the front page and click 3 times on the full moon that shines behind the windmill!
The second clue!You're being chased by the Mewtwo Balls!Solve this riddle and find the next piece of information before they catch up to you!
To find the next clue, search the story page and click three times on Kamex!
The second clue
The third clue!You're being chased by the Mewtwo Balls!Solve this riddle and find the next piece of information before they catch up to you!
Search the character page and click three times on the answer to the riddle shown here!
The third clue
Source:
https://www.pokemon-movie.jp/