Exergames encourage physical activity, but generally require specialized hardware and prescribed activities; whereas pervasive accumulated context exergames (PACEs) allow players to choose their type of exercise, but have limited depth of play. For mass commercialization of PACEs, facilitating long-term behavioural change, we propose two requirements: that PACEs support large-scale and flexible deployment; and that the design of PACEs support staying power through long-term playability. From these requirements, we motivate six PACE design principles and use these principles to develop a multiplayer roleplaying PACE. Results from a week-long study of our game showed that by satisfying the six design principles, we can create a PACE with scalability and staying power. Our results are the first step toward creating PACEs that promotes long-term game engagement, which is needed for activity-related behaviour change.