As we design increasingly complex systems, we run up against fundamental limitations of human imagination. To support practice, it becomes essential to use authentic data and algorithms as design materials to augment designers' intuitions. Recent work has explored some dimensions of using data as a design material, suggesting the contours of a new space of design and prototyping methods. In this paper, we present "Replay Enactments (REs)," an extension of the User Enactments methods that uses data replay as a boundary object, making complex system behavior tangible to designers and stakeholders. We reflect on a set of case studies that have instantiated REs in diverse ways and discuss trade-offs between different ways of using data replays in design. We conclude by highlighting opportunities and challenges for future work. [This paper was published in: "Proceedings of the ACM Designing Interactive Systems Conference (DIS '20)," ACM, 2020, pp. 1607-18.]