  We present the discovery and optical follow-up of the faintest supernova-like
transient known. The event (SN 2019gsc) was discovered in a star-forming host
at 53\,Mpc by ATLAS. A detailed multi-colour light curve was gathered with
Pan-STARRS1 and follow-up spectroscopy was obtained with the NOT and
Gemini-North. The spectra near maximum light show narrow features at low
velocities of 3000 to 4000 km s$^{-1}$, similar to the extremely low luminosity
SNe 2010ae and 2008ha, and the light curve displays a similar fast decline
(\dmr $0.91 \pm 0.10$ mag). SNe 2010ae and 2008ha have been classified as type
Iax supernovae, and together the three either make up a distinct physical class
of their own or are at the extreme low luminosity end of this diverse supernova
population. The bolometric light curve is consistent with a low kinetic energy
of explosion ($E_{\rm k} \sim 10^{49}$ erg s$^{-1}$), a modest ejected mass
($M_{\rm ej} \sim 0.2$ \msol) and radioactive powering by $^{56}$Ni ($M_{\rm
Ni} \sim 2 \times 10^{-3}$ \msol). The spectra are quite well reproduced with
radiative transfer models (TARDIS) and a composition dominated by carbon,
oxygen, magnesium, silicon and sulphur. Remarkably, all three of these extreme
Iax events are in similar low-metallicity star-forming environments. The
combination of the observational constraints for all three may be best
explained by deflagrations of near $M_{\rm Ch}$ hybrid carbon-oxygen-neon white
dwarfs which have short evolutionary pathways to formation.
