  Recently Assef et al.(2018) presented two catalogs of AGN candidates over
30,093 deg^2 selected from the Wide-field Infrared Survey Explorer (WISE)
observations. From their most reliable sample, Assef et al. (2018) identified
45 AGN candidates with the highest variability levels in the AllWISE catalog,
but that are not blazars. Here we present new spectroscopic observations of
some of these targets to further constrain their nature. We also study their
optical lightcurves using observations from CRTS, and find that only seven show
significant optical variability, and that five of those seven are
spectroscopically classified as AGN. In one of them, WISEA J094806.56+031801.7
(W0948+0318), we identify a transient event in the CRTS lightcurve. We present
a detailed analysis of this transient, and characterize it through its CRTS
lightcurve and its multi-wavelength spectral energy distribution obtained from
GALEX, Pan-STARRS and WISE observations. We find that the most likely source of
the transient is a super-luminous supernova (SLSN) in W0948+0318. We estimate
the total radiated energy to be E=1.6\pm 0.3 x 10^52 erg, making it one of the
most energetic SLSN observed. Based on the lack of change in mid-IR color
throughout and after the transient event, we speculate that the location of the
SLSN is within the torus of the AGN. We identify 9 possible analogs to
W0948+0318 based on their WISE lightcurves. None show optically detected
transients and hence suggest significant dust obscuration. Finally, we estimate
a rate of >2x10^-7 yr^-1 per AGN for these transients under the conservative
assumption that none of the identified analogs have a common origin with the
transient in W0948+0318.
