We propose a scheme to generate intense, ultrafast mid-infrared pulses with conversion efficiencies exceeding the upper bound for single-stage difference-frequency mixing as predicted by the Manley-Rowe relations. Finite-element fast Fourier transform simulations of the mixing process show that the parametric cascade downconverter generates 1.7 times more photons (at 10 microm) than in the initial pump pulse (center wavelength of 1.48 microm, duration of 130 fs, and pulse energy of 50 microJ), with negligible pulse spatial and temporal distortion.