  We present a new selection of 358 blue compact dwarf galaxies (BCDs) from
5,000 square degrees in the Dark Energy Survey (DES), and the spectroscopic
follow-up of a subsample of 68 objects. For the subsample of 34 objects with
deep spectra, we measure the metallicity via the direct T$_e$ method using the
auroral [\oiii]$\lambda$ 4363 emission line. These BCDs have an average oxygen
abundance of 12+log(O/H)= 7.8, with stellar masses between 10$^7$ to 10$^8$
M$_\odot$ and specific star formation rates between $\sim$ 10$^{-9}$ to
10$^{-7}$ yr$^{-1}$. We compare the position of our BCDs with the
Mass-metallicity (M-Z) and Luminosity-metallicity (L-Z) relation derived from
the Local Volume Legacy sample. We find the scatter about the M-Z relation is
smaller than the scatter about the L-Z relation. We identify a correlation
between the offsets from the M-Z and L-Z relation that we suggest is due to the
contribution of metal-poor inflows. Finally, we explore the validity of the
mass-metallicity-SFR fundamental plane in the mass range probed by our
galaxies. We find that BCDs with stellar masses smaller than
$10^{8}$M$_{\odot}$ do not follow the extrapolation of the fundamental plane.
This result suggests that mechanisms other than the balance between inflows and
outflows may be at play in regulating the position of low mass galaxies in the
M-Z-SFR space.
