The influence of the N-2-to-total (N-2 + Ar) ratio (R-N) on the structure and properties of duodenary (TiVCrZrNbMoHfTaWAlSi)N coatings with markedly high mixing entropy is investigated. The coatings are deposited by DC reactive magnetron sputtering with an equimolar (TiVCrZrNbMoHfTaWAlSi)N target. No external bias and heating are applied to the substrate. An increase in R-N contributes to an increase in N concentration, residual stress, and lattice parameter. At low R-N, the coatings have an amorphous structure. When R-N is 15%, an FCC nanocrystal structure with (200)-preferred orientation appears. When R-N increases to 20%, HCP nitride nanocrystals coexist with coarse columnar grain FCC structures with (111)-preferred orientation. As R-N increases to 50%, the grain size decreases, and their preferred FCC orientation returns to (200). Given that the mechanical and electro-optical properties are strongly correlated with R-N, the hardness of the coatings is enhanced up to 34.8 GPa. However, the electrical conductivity and light reflectivity at 0.62 eV deteriorate from 5319 S/cm to 62.1 S/cm and from 71.2% to 42.8%, respectively. These results provide a valuable basis for the future development of high-entropy nitrides.