The electron transmission over an oscillating quantum well is studied perturbatively and numerically in the phase-coherent regime. The dynamically induced multichannel situation gives rise to a pronounced asymmetric resonance and antiresonance structure. The Fano line obtained is attributed to the interaction of the raised virtual discrete energy level with the continuum. Interestingly, the unitarity condition imposes the restriction that the transmission coefficients vanish altogether at the zero energies, leading to the concept of an electronic mirror.