  Active galactic nuclei (AGNs) are known to exhibit optical/UV variability and
most of them can be well modeled by the damped random walks. Physical processes
that are not related to the accretion disk, such as tidal disruption events
(TDE) or moving foreground dusty clouds, can cause flare-like and eclipse-like
features in the optical light curve. Both long-term and high-cadence monitoring
are needed to identify such features. By combining the Sloan Digital Sky Survey
(SDSS), Panoramic Survey Telescope, and Rapid Response System (Pan-STARRS) with
the Zwicky Transient Facility (ZTF) survey, we are able to identify a rare
sample (11) out of the SDSS quasar catalog (around 83, 000). These quasars
exhibit more or less constant brightness but show rapid optical variation in
the ZTF DR2 epochs. To investigate the possible origins of these
flare/eclipse-like variabilities, we propose the second epoch spectroscopic
observations with the Gran Telescopio CANARIAS (GTC). We find that the change
in accretion rate plays a significant role in these quasar variabilities. Among
them, we identify two Changing-Look Active Galactic Nuclei (CL-AGN) candidates:
SDSS J1427+2930 and SDSS J1420+3757. The luminosity change of the former may be
caused by the enhanced SMBH accretion or the tidal disruption event, while the
latter is more related to the change in the accretion rate.
