  The discovery of the ultra-diffuse galaxy NGC 1052-DF2 and its peculiar
population of star clusters has raised new questions about the connections
between galaxies and dark matter halos at the extremes of galaxy formation. In
light of debates over the measured velocity dispersion of its star clusters and
the associated mass estimate, we constrain mass models of DF2 using its
observed kinematics with a range of priors on the halo mass. Models in which
the galaxy obeys a standard stellar-halo mass relation are in tension with the
data and also require a large central density core. Better fits are obtained
when the halo mass is left free, even after accounting for increased model
complexity. The dynamical mass-to-light ratio for our model with a weak prior
on the halo mass is $1.7^{+0.7}_{-0.5} \ M_\odot / L_{\odot, V}$, consistent
with the stellar population estimate for DF2. We use tidal analysis to find
that the low-mass models are consistent with the undisturbed isophotes of DF2.
Finally we compare with Local Group dwarf galaxies and demonstrate that DF2 is
an outlier in both its spatial extent and its relative dark matter deficit.
