  We report follow-up observations of the Sloan Digital Sky Survey Cataclysmic
Variable SDSS J210014.12+004446.0 (hereafter SDSS J2100). We obtained
photometry and spectroscopy in both outburst and quiescent states, providing
the first quiescent spectrum of this source. In both states, non-sinusoidal
photometric modulations are apparent, suggestive of superhumps, placing SDSS
J2100 in the SU UMa subclass of dwarf novae. However, the periods during
outburst and quiescence differ significantly, being 2.099 plus or minus 0.002
hr and 1.96 plus or minus 0.02 hr respectively. Our phase-resolved spectroscopy
during outburst yielded an estimate of about 2 hr for the orbital period,
consistent with the photometry. The presence of the shorter period modulation
at quiescence is unusual, but not unique. Another atypical feature is the
relative weakness of the Balmer emission lines in quiescence. Overall, we find
a close similarity between SDSS J2100 and the well-studied superhump
cataclysmic Variable V503 Cygni. By analogy, we suggest that the quiescent
modulation is due to a tilted accretion disk -- producing negative superhumps
-- and the modulation in outburst is due to positive superhumps from the
precession of an elliptical disk.
