Multi-wavelength light curves of the afterglow emission of GRB 160821B for different electromagnetic bands as labeled. The observational data are taken from (Lamb et al. 2019; Troja et al. 2019) and Swift. The dotted, dash-dotted, dashed, and solid lines correspond to the emission from the jet external shock, the thermal kilonova, the PWN, and their combination, respectively. The insert shows the early X-ray afterglow plateau, which may indicate the remnant NS could intrinsically be a magnetar before its surface magnetic field is buried.