  Broad absorption line (BAL) features in quasar spectra reveal an unambiguous
signature of energetic outflows from central supermassive black holes, and thus
BAL quasars are prime targets for investigating the potential process of
luminous quasar feedback on galaxies. We analyzed the rest-UV spectrum of an
"overlapping trough" iron low-ionization broad absorption line quasar (FeLoBAL)
SDSS J135246.37+423923.5 using the novel spectral synthesis code SimBAL
(Leighly et al. 2018) and discovered an extraordinarily fast and energetic BAL
outflow. Our analysis revealed outflow velocities reaching $\sim -38000\rm \,
km\, s^{-1}$ with a velocity width of $\sim 10000\rm \, km\, s^{-1}$ which is
the largest FeLoBAL outflow velocity measured to date. The column density of
the outflow gas is log$N_H\sim23.2\,[\rm cm^{-1}]$ with the log kinetic
luminosity $\log L_{KE}\sim48.1$ [erg $\rm s^{-1}$] which exceeds the
bolometric luminosity of the quasar and is energetic enough to effectively
drive quasar feedback. The energy estimate for the outflow is far greater than
the estimates from any BAL object previously reported.
  The object also shows "anomalous reddening" and a significant scattered
component that we were able to model with SimBAL. We found the first definitive
case for radiation filtering in an additional zero-velocity absorption
component that required an absorbed continuum to produce the particular
absorption lines observed (MgII, AlIII and AlII) without also producing the
high ionization lines such as CIV.
