In a nutshell, the King's Keys deck started as an experiment to see what card games would be like if you rebuilt playing cards from the ground up. Instead of using ranks and suits, each card has a number (from one to four), one of four items, and one of four colors. The result is what I call a 4x4x4 deck where 64 playing cards each have a unique combination of these three parts.

12 Tenets of Board Game Design for Stonemaier Games