  We report the analysis of the microlensing event OGLE-2018-BLG-0677. A small
feature in the light curve of the event leads to the discovery that the lens is
a star-planet system. Although there are two degenerate solutions that could
not be distinguished for this event, both lead to a similar planet-host mass
ratio. We perform a Bayesian analysis based on a Galactic model to obtain the
properties of the system and find that the planet corresponds to a
super-Earth/sub-Neptune with a mass $M_{\mathrm{planet}} =
{3.96}^{+5.88}_{-2.66}\mathrm{M_\oplus}$. The host star has a mass $
M_{\mathrm{host}} = {0.12}^{+0.14}_{-0.08}\mathrm{M_\odot}$. The projected
separation for the inner and outer solutions are ${0.63}^{+0.20}_{-0.17}$~AU
and ${0.72}^{+0.23}_{-0.19}$~AU respectively. At $\Delta\chi^2=\chi^2({\rm
1L1S})-\chi^2({\rm 2L1S})=46$, this is by far the lowest $\Delta\chi^2$ for any
securely-detected microlensing planet to date, a feature that is closely
connected to the fact that it is detected primarily via a "dip" rather than a
"bump".
