Faint Mg II absorber galaxy revealed in the DECaLS residual images. These galaxies remained undetected in DECaLS photometry due to the glare of the bright quasar. Each panel shows the g (blue), r (green), z (red) band colour composite inverted-image centred on the quasar (grey contour), marked as star, and the SDSS fibre of radius 1.5 arcsec (dotted circle). The associated Mg II absorption and [O II] λλ3727, 3729 nebular emission line profiles are shown in the bottom left and right insets, respectively.