High performance millimeter wave absorbers were developed by the uneven distribution of lossy particles like conducting multiwall carbon nanotubes (MWNTs) and magnetic ultra-small ferrite (Fe3O4) particles (of 2-3 nm) nucleated on reduced graphene oxide sheets (rGO-Fe3O4) in biphasic polymeric blends of polycarbonate (PC) and poly(styrene -co-acrylonitrile (SAN). This acted as micro-absorbers manifesting outstanding millimeter wave absorption (85.5%). The strategy of nucleating magnetic ferrites of 2-3 nm size on rGO sheets resulted in high coercive field; a characteristic of hard magnets. The detailed millimeter wave attenuation mechanism was investigated using various electromagnetic parameters in biphasic blends containing various microwave active nanoparticles like (i) MWNTs, (ii) rGO-Fe3O4 and a combination of (iii) MWNTs and Fe3O4 as well as (iv) MWNTs and rGO-Fe3O4. The primary mechanism of millimeter wave attenuation in PC composites was reflection whereas in case of blends the attenuation was mostly through absorption mechanism. This is corresponding to the selective localization of nanoparticles in PC phase manifesting heterogeneous dielectric media with multiple interfaces. In order to enhance absorption, the surface reflection of millimeter wave was minimized by high surface resistivity whereas the absorption was facilitated by high bulk electrical conductivity (5 S/cm) in combination with the lossy inclusions through multiple scattering. Herein, the blends consisting of both MWNTs and rGO-Fe3O4 depicted a total shielding effectiveness of -34.1 dB (at 18 GHz) manifesting 99.96% attenuation of the incoming millimeter wave radiation. Taken together all the microwave attenuation parameters, it is revealed that the unique structure of blends and selective localization of nanoparticles associated with engineered nanoparticle results in extraordinary synergy in millimeter wave absorption.