NUV spectrum of PS16dtm (magenta) obtained with HST using STIS/NUV-MAMA. Also shown are the blue end of the MagE spectrum of PS16dtm (black) and NUV spectra of several comparison objects, including TDEs, BAL QSOs, SNe IIn, and an NLS1 galaxy. The rest wavelength of Mg II is marked. Along with BAL QSOs and PS1-11af, PS16dtm shows broad (∼10,000 km s⁻¹) blueshifted Mg II absorption.