  In this paper we present spectroscopic and photometric observations for four
core collapse supernovae (SNe), namely SNe 1994N, 1999br, 1999eu and 2001dc.
Together with SN 1997D, we show that they form a group of exceptionally
low-luminosity events. These SNe have narrow spectral lines (indicating low
expansion velocities) and low luminosities at every phase (significantly lower
than those of typical core-collapse supernovae). The very low luminosity during
the ^{56}Co radioactive decay tail indicates that the mass of ^{56}Ni ejected
during the explosion is much smaller (M(Ni) ~ 2-8 x 10^{-3} Mo) than the
average (M(Ni) ~ 6-10 x 10^{-2} Mo). Two supernovae of this group (SN 1999br
and SN 2001dc) were discovered very close to the explosion epoch, allowing us
to determine the lengths of their plateaux (~ 100 days) as well as
establishiing the explosion epochs of the other, less-completely observed SNe.
It is likely that this group of SNe represent the extreme low-luminosity tail
of a single continuous distribution of SN II-P events. Their kinetic energy is
also exceptionally low. Although an origin from low mass progenitors has also
been proposed for low-luminosity core-collapse SNe, recent work provides
evidence in favour of the high mass progenitor scenario. The incidence of these
low--luminosity SNe could be as high as 4-5$ $ of all type II SNe.
