To address the issue of low-frequency oscillations in active power and frequency caused by parameter mismatches among multiple grid-forming energy-storage converters in islanded microgrids—where the fixed damping coefficient of conventional VSG control fails to simultaneously achieve satisfactory dynamic response and steady-state accuracy—this paper proposes a VSG control strategy enhanced by cooperative transient damping. The strategy first introduces active power feedback transient damping (TDP) into the active power loop. Although TDP can effectively suppress low-frequency oscillations in active power, it provides insufficient suppression for frequency oscillations induced by angular frequency coupling. Therefore, angular frequency feedback compensation is further incorporated, forming an active power-angular frequency two-degree-of-freedom architecture. This design flexibly adjusts the system damping without compromising steady-state performance, achieving cooperative suppression of both types of oscillations. Simulation and experimental results demonstrate that the proposed strategy significantly suppresses low-frequency oscillations in active power and frequency, effectively improving both the dynamic response performance and steady-state accuracy of the system.