  We analyze a $\Delta V\sim-9$ magnitude flare on the newly identified M8
dwarf SDSS J022116.84+194020.4 (hereafter SDSSJ0221) detected as part of the
All-Sky Automated Survey for Supernovae (ASAS-SN). Using infrared and optical
spectra, we confirm that SDSSJ0221 is a relatively nearby (d$\sim$76 pc) M8
dwarf with strong quiescent H$\alpha$ emission. Based on kinematics and the
absence of features consistent with low-gravity (young) ultracool dwarfs, we
place a lower limit of 200 Myr on the age of SDSSJ0221. When modeled with a
simple, classical flare light-curve, this flare is consistent with a total
$U$-band flare energy $E_U\sim$ 10$^{34}$ erg, confirming that the most
dramatic flares are not limited to warmer, more massive stars. Scaled to
include a rough estimate of the emission line contribution to the $V$ band, we
estimate a blackbody filling factor of $\sim$$10-30\%$ during the flare peak
and $\sim$$0.5-1.6\%$ during the flare decay phase. These filling factors
correspond to flare areas that are an order of magnitude larger than those
measured for most mid-M dwarf flares.

Solar and Stellar Astrophysics