  We present a new end-to-end pipeline for Mock Observations of X-ray Halos and
Analysis (MOXHA) for hydrodynamic simulations of massive halos, and use it to
investigate X-ray scaling relations and hydrostatic mass bias in the Simba
cosmological hydrodynamic simulation for halos with $M_{500}\sim
10^{13-15}M_\odot$. MOXHA ties together existing yT-based software packages and
adds new functionality to provide an end-to-end pipeline for generating mock
X-ray halo data from large-scale or zoom simulation boxes. We compare
MOXHA-derived halo properties in Simba to their emission-weighted counterparts,
and forecast the systematic mass bias in mock Athena observations. Overall, we
find inferred hydrostatic masses are biased low compared to true Simba values.
For simple mass-weighting, we find $b_\text{MW} = 0.15^{+0.15}_{-0.14}$
($16-84\%$ range), while emission-weighting increases this to
$b_\text{LW}=0.30^{+0.19}_{-0.10}$. The larger bias versus mass-weighted values
we attribute to the spectroscopic and emission-weighted temperatures being
biased systematically lower than mass-weighted temperatures. The full MOXHA
pipeline recovers the emission-weighted hydrostatic masses at $R_{500}$
reasonably well, yielding $b_\text{X}=0.33^{+0.28}_{-0.34}$. MOXHA-derived halo
X-ray scalings are in very good agreement with observed scaling relations, with
the inclusion of lower-mass groups significantly steepening the
$L_\text{X}-M_{500}$, $M_{500}-T_\text{X}$, and $L_\text{X}-T_\text{X}$
relations. This indicates the strong effect the Simba feedback model has on
low-mass halos, which strongly evacuates poor groups but still retains enough
gas to reproduce observations. We find similar trends for analogous scaling
relations measured at $R_{500}$, as expected for halo-wide gas evacuation.
