Mixed reality (MR) games refer to games that integrate physical entities with digitally mediated contents. Currently, it entails game creators to integrate heterogeneous virtual and physical components, which is often time-consuming and labor-intensive, without the support of a coherent technology stack. The underlying technodiversity manifested by the research corpus suggests a complicated, multi-dimensional design space that goes beyond merely technical concerns. In this research, we adopted a research-through-design approach and proposed an MR game technology stack that facilitates flexible, low-code game development. As design grounding, we first surveyed 34 state-of-the-art studies, and results were synergized into three different spectra of technological affordances, respectively activity range, user interface and feedback control, to inform our next design process. We then went through an iterative prototyping phase and implemented an MR game development toolset. A co-design workshop was conducted, where we invited 15 participants to try the prototype tools and co-ideate the potential use scenarios for the proposed technology stack. First-hand user feedback was collected via questionnaires and semi-structured interviews. As a result, four conceptual game designs with three major design implications were generated, which conjointly reflect a broader understanding on MR gameful experience and contribute fresh insights to this emerging research domain.