  The Dark Energy Spectroscopic Instrument Milky Way Survey (DESI MWS) will
explore the assembly history of the Milky Way by characterising remnants of
ancient dwarf galaxy accretion events and improving constraints on the
distribution of dark matter in the outer halo. We present mock catalogues that
reproduce the selection criteria of MWS and the format of the final MWS data
set. These catalogues can be used to test methods for quantifying the
properties of stellar halo substructure and reconstructing the Milky Way's
accretion history with the MWS data, including the effects of halo-to-halo
variance. The mock catalogues are based on a phase-space kernel expansion
technique applied to star particles in the Auriga suite of six high-resolution
$\Lambda$CDM magneto-hydrodynamic zoom-in simulations. They include photometric
properties (and associated errors) used in DESI target selection and the
outputs of the MWS spectral analysis pipeline (radial velocity, metallicity,
surface gravity, and temperature). They also include information from the
underlying simulation, such as the total gravitational potential and
information on the progenitors of accreted halo stars. We discuss how the
subset of halo stars observable by MWS in these simulations corresponds to
their true content and properties. These mock Milky Ways have rich accretion
histories, resulting in a large number of substructures that span the whole
stellar halo out to large distances and have substantial overlap in the space
of orbital energy and angular momentum.
