Pokémon Pokopia requires 27 Mysterious Slates to solve the Mew mural puzzle.
The slates are found at treasure spots throughout the game. Each one corresponds to part of a larger image, and its reverse side provides information about the Unown position associated with that piece.
Players must take the slates to the ruins in Withered Wastelands and arrange them correctly to complete the mural. Once the image is assembled, Mew appears in front of it and can be befriended.
The number 27 is significant to the puzzle’s structure because the mural uses a 3-by-3 arrangement of nine groups, each represented through three related slate positions. This is separate from the ordinary habitat system and is not the same as finding Mew randomly on a Dream Island.