Several more cards from the Pokémon Go TCG special set have been revealed! The cards were revealed simultaneously by the English and Japanese Pokémon websites.
New Ditto Mechanics
Just like in Pokémon Go, Ditto will only appear as another Pokémon.
Some cards will appear to be a normal Pokémon but are actually stickers! When you peel them off, the real card will appear: Ditto.
To know which cards are Ditto, the cards of this type will have a ditto in the lower left corner. Cards with a sticker cannot be used in official competitions. 
Video explaining the mechanics