The NPC cards is a deck of cards that will contain the game stats of all the NPCs in the book (around 40). The cards will be in PDF, with the same size as standard playing cards. Backers who pledged for this reward will get a code to order a printed version of the cards if they wish. Backers will have pay at cost the base printing and shipping costs of the cards at DriveThruRPG (around $4 US for the printing).
Don't see the answer to your question? Ask the project creator directly.