We theoretically investigate the induced transparency phenomenon in a hybrid double-cavities magnon-optomechanical system. A ferromagnetic material yttrium iron garnet (YIG) sphere and a mechanical resonator are placed in one of the microwave cavities, and the other is coupled to a mechanical phonon. We observe not only magnetically induced transparency (MIT) generated by magnon–photon interaction, but also magnomechanically induced transparency (MMIT) produced by nonlinear phonon–magnon interaction. It is shown that better transparency effect is obtained by appropriately adjusting the tunneling coupling strength. The effect of the interaction of the two mechanical resonators with the two microwave cavities on the output spectrum is discussed separately. In addition, we have established a new scheme to measure the mechanical phonon–photon coupling strength. We also investigated the effect of the cavity decay rate on the output field and found that better transparency can be obtained by appropriately reducing the decay rate of the cavity. We further explored the fast and slow light conversion phenomenon. These results have potential applications in quantum information processing and high precision measurements.