The Dream Cards are the soot rendered cards which depict the nightmares and the Decryptions are the word cards. The basic rule of the game constitutes the participants playing their Decryption, which they think best mocks a Dream Card dealt every round.
Like dreams/nightmares, soot does not settle collectively all together. Some of it escapes. People do not remember their dreams as a whole. They only remember key scary elements. Hence, soot was the appropriate channel to represent nightmares. It also renders the nightmarish quality.
It is a pack of 70 cards, combining Dream and Word cards. It also has a set of rules explaining the game to the users.