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We report magnetoelastic (0.46%) features and giant frequency dispersion (Δω ∼ 317 rad/s, ΔT ∼ 34 K) of ac-magnetic susceptibility (χ_ac) (ω,T)) at two distinct temperatures (T_P1-ac = 144 K and T_P2-ac = 211 K) in Cr and Fe co-substituted MnCo₂O₄ cubic (Fd<over bar>3m) spinel forming the composition Cr_0.2Mn_0.8Fe_0.4Co_1.6O₄. A detailed temperature dependence of neutron and synchrotron x-ray diffraction studies reveal anomalous changes in the lattice parameter across ferrimagnetic (FiM) ordering (T_C = 260 K), as well as at two additional transitions T_S1 ∼ 114 K and T_S2 similar to 173 K. Competing antiferromagnetic exchange interactions among the cations (J_AA/k_B = 23.2 K, J_BB/k_B = 9.15 K, and J_AB/k_B = 25.25 K) are responsible for the giant frequency dispersion observed in χ_ac(ω, T), while ruling out the presence of a conventional spin-glass state below T_C. The Kubelka Munk analysis of the optical absorbance data is used to find the optical band gap of 1.16 eV (E_g). The optical absorption spectrum reveals well defined d-d transitions attributed to the charge transfer in this investigated system. Such substantial red-shift compared to the pristine _p-type semiconducting Co₃O₄ together with the FiM behavior of this compound may open a constructive approach for applications in magneto electronics.