Policy participation requires a democratic decision-making process, though typical co-design approaches focus more on immersing participants in the design process and facilitating creative thinking. This research proposes a new concept of policy co-design workshops to ensure both policy and co-design values. The feasibility and acceptability of policy ideas were found to be key requirements in policy co-design. The requirements were designed to be fulfilled through a gamified policy co-design workshop - Policy Puzzle Game - with a jigsaw puzzle-style toolkit and process. The game was used in real policy development by a municipal government with participating citizens, activists, civil servant s, and design thinking facilitators. The major findings from post-workshop interviews include insights on the engagement process of the game, the unique roles of different stakeholder groups, and their contributions to making policy ideas feasible and acceptable. Based on the findings, possibilities for further application of the game and the significance of the research are discussed.