  The use of realistic mock galaxy catalogues is essential in the preparation
of large galaxy surveys, in order to test and validate theoretical models and
to assess systematics. We present an updated version of the mock catalogue
constructed from the Millennium-XXL simulation, which uses a halo occupation
distribution (HOD) method to assign galaxies r-band magnitudes and g-r colours.
We have made several modifications to the mock to improve the agreement with
measurements from the SDSS and GAMA surveys. We find that cubic interpolation,
which was used to build the original halo lightcone, produces extreme
velocities between snapshots. Using linear interpolation improves the
correlation function quadrupole measurements on small scales. We also update
the g-r colour distributions so that the observed colours better agree with
measurements from GAMA data, particularly for faint galaxies. As an example of
the science that can be done with the mock, we investigate how the luminosity
function depends on environment and colour, and find good agreement with
measurements from the GAMA survey. This full-sky mock catalogue is designed for
the ongoing Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey
(BGS), and is complete to a magnitude limit r=20.2.
