  The moir\'e pattern induced by lattice mismatch in transition-metal
dichalcogenide heterobilayers causes the formation of flat bands, where
interactions dominate the kinetic energy. At fractional fillings of the flat
valence band, the long-range electron interactions then induce Wigner-Mott
crystals. In this Letter we investigate the nontrivial electronic phases
appearing away from commensurate fillings. Here, competing phases arise that
are either characterized as doped Wigner-Mott charge transfer insulators or
alternatively, a novel state with frozen charge order yet is conducting: the
'electron slush'. We propose that an extremely spatially inhomogeneous local
density of states can serve as a key signature of the electron slush.
