  A fraction of active galactic nuclei (AGN) exhibit dramatic variability,
which is observed on timescales down to minutes in the X-ray band. We introduce
the case study of 1H 1934-063 (z = 0.0102), a Narrow-line Seyfert 1 (NLS1)
among the brightest and most variable AGN ever observed with XMM-Newton. This
work includes spectral and temporal analyses of a concurrent XMM-Newton and
NuSTAR 2015 observation lasting 130 kiloseconds, during which the X-ray source
exhibited a steep (factor of 6) plummet and subsequent full recovery of flux
level, accompanied by deviation from a single log-normal flux distribution. We
rule out Compton-thin obscuration as the cause for this dramatic variability
observed even at NuSTAR energies. In order to constrain coronal geometry,
dynamics, and emission/absorption processes, we compare detailed spectral
fitting with Fourier-based timing analysis. Similar to other well-studied,
highly variable Seyfert 1s, this AGN is X-ray bright and displays strong
reflection features. We find a narrower broad iron line component compared to
most Seyfert 1s, and constrain black hole spin to be < 0.1, one of the lowest
yet discovered for such systems. Combined spectral and timing results are
consistent with a dramatic change in the continuum on timescales as short as a
few kiloseconds dictating the nature of this variability. We also discover a
Fe-K time lag, measuring a delay of 20 seconds between relativistically-blurred
reflection off the inner accretion flow and the hard X-ray continuum emission.
