  Aims: We aim to confirm whether the eclipsing cataclysmic variable V902 Mon
is an Intermediate Polar, to characterise its X-ray spectrum and flux, and to
refine its orbital ephemeris and spin period. Methods: We performed
spectrographic observations of V902 Mon in 2016 with the 2.2m Calar Alto
telescope, and X-ray photometry and spectroscopy with XMM-Newton in October
2017. This data was supplemented by several years of AAVSO visual photometry.
Results: We have confirmed V902 Mon as an IP based on detecting the spin
period, with a value of 2,208s, at multiple epochs. Spectroscopy of the donor
star and Gaia parallax yield a distance of 3.5+1.3-0.9, kpc, suggesting an
X-ray luminosity one or two orders of magnitude lower than the 10^33 erg/s
typical of previously known IPs. The X-ray to optical flux ratio is also very
low. The inclination of the system is more than 79deg, with a most likely value
of around 82deg. We have refined the eclipse ephemeris, stable over 14,000
cycles. The Halpha line is present throughout the orbital cycle and is clearly
present during eclipse, suggesting an origin distant from the white dwarf, and
shows radial velocity variations at the orbital period. The amplitude and
overall recessional velocity seem inconsistent with an origin in the disc. The
\emph{XMM-Newton} observation reveals a partially absorbed plasma model typical
of magnetic CVs, with a fluorescent iron line at 6.4keV showing a large
equivalent width of 1.4keV. Conclusions: V902 Mon is an IP, and probably a
member of the hypothesized X-ray underluminous class of IPs. It is likely to be
a disc accretor, though the radial velocity behaviour of the Halpha line
remains puzzling. The large equivalent width of the fluorescent iron line, the
small FX/Fopt ratio, and the only marginal detection of X-ray eclipses suggests
that the X-ray emission arises from scattering.
