Systematic inelastic neutron scattering studies have been performed on La1.85Sr0.15Cu1-yNiyO4 in order to elucidate the microscopic mechanism of magnetic Ni impurity doping effects on spin dynamics and superconductivity. In contrast to Zn doping, which precipitates static or quasistatic spin correlations around dopant, Ni doping remarkably reduces E-comme, the minimum energy of the upward branch of the hourglass-shaped magnetic dispersion where a commensurate magnetic peak is observed. Ni doping at y similar to 0.04 further reduces E-comme to zero energy and broadens the distribution of E-comme, corresponding to the appearance of the normal state at base temperature (T similar to 4 K) as well as the broadening of the superconducting transition.