Decreasing accretion and outflow in the peculiar eruptive young star V899 Mon

V899 Mon is an eruptive young star showing characteristics of both FUors and EXors. It reached a peak brightness in 2010, then briefly faded in 2011, followed by a second outburst. We conducted multi-filter optical photometric monitoring, as well as optical and near-infrared spectroscopic observations of V899 Mon. The light curves and color-magnitude diagrams show that V899 Mon has been gradually fading after its second outburst peak in 2018, but smaller accretion bursts are still happening. Our spectroscopic observations taken with Gemini/IGRINS and VLT/MUSE show many emission lines, unlike during the outbursting stage. We used the emission line fluxes to estimate the accretion rate and found that it significantly decreased. The mass loss rate is also weakening. With spectro-astrometric methods, we discovered that the forbidden emission lines trace a jet emanating from V899 Mon. On the other hand, permitted metallic lines and the CO bandhead emission can be modeled well with a disk in Keplerian rotation, which also gives a tight constraint for the dynamical stellar mass. We suggest that V899 Mon has almost finished its second outburst and is returning to the quiescent phase. We discuss what physical changes led to the observed properties of V899 Mon.