Herein, it is reported the concomitant synthesis and sintering in a single step of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg), a spinel-structured high-entropy oxides, by the reactive flash sintering technique. A single phase, identified with a spinel crystal structure Fd3m, was obtained in just 30 min at a furnace temperature of 1173 K. The structural and magnetic properties of the prepared compounds were assessed by the combined use of various techniques, aiming to understand the correlations between functional properties and crystal structure. Characteristic features of the Mossbauer spectra prove the existence of different nonequivalent Fe environments . Both compositions display soft magnetic behavior, characterized by low coercive fields and saturation magnetization reached at low fields. Thus, the substitution of nonmagnetic Mg2+ for magnetic Fe2+ results in a decrease in magnetic parameters due to the weakening of the super-exchange interaction among the magnetic moments.