Abstract: Games have become established tools within participatory urban planning practice that provide safe spaces for collective actions such as deliberation, negotiation of conflicting agendas, scenario testing, and collaborative worldbuilding. While a body of literature on the effectiveness of games to address complex urban planning issues is emerging, significantly less literature addresses the design and development process of serious games with a possible space in its own right within urban planning practice. Our study investigates long term iterative processes of designing a game for visioning urban futures, specifically, how design iterations connect to the application of games in practice by accommodating or responding to emerging needs, goals, and relationships. We approach this topic through the case study of the Sustainability Futures Game, a game designed by the Helsinki-based creative agency Hellon to support business leaders, sustainability specialists, and city officials to imagine desirable alternative urban futures. Through storytelling and collective worldbuilding, players first imagine what sustainable urban living means for a specific city, frame their vision using the UN’s sustainable development goals, and finally create concrete pathways towards reaching these goals. This article uses a genealogical approach to systematically analyse the five design iterations of the Sustainability Futures Game. It aims to elucidate the contextual and relational influences on the application of serious games in urban planning practice to understand how these influences might encourage or inhibit their potential to foster transformation towards sustainable futures.