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Nitrides with novel compositions are an emerging research topic in basic energy science, with applications in optoelectronics, catalysis, and magnetism. Ternary semiconductors are underexplored and have unique properties, such as transitions between cation ordered and disordered structures, which may be exploited to modify properties in a single composition. We demonstrate combinatorial co-sputtering of a new II-IV-N₂, MgSnN₂, in a phase-pure wurtzite structure across a range of cation compositions and from 200 to 400 °C. Below 200 °C, a metastable rocksalt phase is observed which is a potential wide bandgap, high dielectric constant material. Ellipsometry reveals an optical absorption onset at ~2 eV for the wurtzite phase, suggesting tuning via cation disorder from the predicted bandgap of 2.5 eV; disorder is confirmed by synchrotron x-ray diffraction. Finally, we demonstrate epitaxial growth via combinatorial co-sputtering on GaN. Based on this work, MgSnN₂ is a target for fundamental exploration of novel nitride properties as well as a candidate for future device applications.