In this paper, we discuss our approach to designing a board game, the Green Economy, that promotes systems thinking. We anchored our game design process on design-by-analogy and rapid prototyping concepts by taking a modular approach to overcome the trade-off between realism and simplicity. The unique feature of the Green Economy enables players to change the rules of the game during the gameplay, which gives them a partial design opportunity. The theme, sustainable development, was chosen to challenge the players' systems thinking in sustainable development. Systems thinking enables us to understand and face the complex challenges in global and networked social structures. Our design experience demonstrates the benefit of designing dynamic game elements that involve both strategic gameplay and game (re)design through systems thinking.