We share our experiences using an "unplugged" card game to introduce youth and adults to fundamental coding concepts and computational thinking (CT). In this game, players develop algorithmic thinking and understanding of constructs such as loops and conditional statements as they build and execute battle plans ("code") in a pirate-themed card game. There are two factors that influence the game's impact on learning: design and implementation. We describe how the game was designed to teach coding and CT, what actually happened when we tested it in outreach programs and in schools, and how we improved the connection between theoretical and actual effectiveness. One challenge was to improve the efficiency of teaching rules. Theoretically, players gain and master CT skills as they pursue game goals, but only when they correctly operate within the rule system. In practice, we saw that teaching the rules was taking an inordinate amount of time with diminishing returns as players became cognitively overloaded. Over several implementations, we generalized design principles that work for groups of different characteristics, including ages, size, and learning contexts. A key heuristic was to modify the game to introduce a practice round with reduced rules while not sacrificing playability. We also describe some gaps between play and learning that we could not bridge with the game alone, which revealed both its limitations and the importance of additional facilitation necessary to support learning.