  Studying the galaxies responsible for reionization is often conducted through
local reionization-era analogs; however, many of these local analogs are too
massive to be representative of the low-mass star-forming galaxies that are
thought to play a dominant role in reionization. The local, low-mass dwarf
starburst galaxy Pox 186 is one such system with physical conditions
representative of a reionization-era starburst galaxy. We present deep
ultraviolet (UV) spectroscopy of Pox 186 to study its stellar population and
ionization conditions and to compare these conditions to other local starburst
galaxies. The new Cosmic Origins Spectrograph data are combined with archival
observations to cover $\sim$1150-2000 A and allow for an assessment of Pox
186's stellar population, the relative enrichment of C and O, and the escape of
ionizing photons. We detect significant Ly$\alpha$ and low-ionization state
absorption features, indicative of previously undetected neutral gas in Pox
186. The C/O relative abundance, log(C/O) = -0.62$\pm$0.02, is consistent with
other low-metallicity dwarf galaxies and suggests a comparable star formation
history in these systems. We compare UV line ratios in Pox 186 to those of
dwarf galaxies and photoionization models, and we find excellent agreement for
the ratios utilizing the intense C III], O III], and double-peaked C IV lines.
However, the UV and optical He II emission is faint and distinguishes Pox 186
from other local starburst dwarf galaxies. We explore mechanisms that could
produce faint He II, which have implications for the low-mass reionization-era
galaxies which may have similar ionization conditions.
