This deck by De'Vo Playing Cards, one of the pioneers in creating proper cardistry decks, has found a fitting name in 'WTF', as it has an astounding number of different functions and uses.
First of all, it's a double-sided cardistry deck with a white and black side, allowing fans in both colours as well as a fan in alternating black-and-white. Besides that, every card's black and white side features a letter which allows you to make words.
The possibilities for an experienced magician or cardist are numerous. For instance, try surprising your spectators by spelling out a word or sentence with your cards.