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 $Deltachi^2=chi^2({rm 1L1S})-chi^2({rm 2L1S})=46$, this is by far the lowest $Deltachi^2$ 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.
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