  We investigate the implications of the dark axion portal interaction, the
axion-photon-dark photon vertex, for the future experiments SHiP and FASER. We
also study the phenomenology of the combined vector portal (kinetic mixing of
the photon and dark photon) and dark axion portal. The muon $g-2$ discrepancy
is unfortunately not solved even with the two portals, but the low-energy beam
dump experiments with monophoton detection capability can open new
opportunities in light dark sector searches using the combined portals.
