  Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects
with X-ray luminosities above 10$^{39}$ erg s$^{-1}$. The average number of
ULXs per galaxy is still not well constrained, especially given the uncertainty
on the fraction of ULX transients. Here, we report the identification of a new
transient ULX in the galaxy NGC 55 (which we label as ULX-2), thanks to recent
XMM-Newton and the Neil Gehrels Swift Observatory observations. This object was
previously classified as a transient X-ray source with a luminosity around a
few 10$^{38}$ erg s$^{-1}$ in a 2010 XMM-Newton observation. Thanks to new and
deeper observations ($\sim$ 130 ks each), we show that the source reaches a
luminosity peak $>1.6 \times 10^{39}$ erg s$^{-1}$. The X-ray spectrum of ULX-2
is much softer than in previous observations and fits in the class of soft
ULXs. It can be well described using a model with two thermal components, as
often found in ULXs. The time scales of the X-ray variability are of the order
of a month and are likely driven by small changes in the accretion rate or due
to super-orbital modulations, attributed to precession of the accretion disc,
which is similar to other ULXs.
