  We describe the time-dependent properties of a new spectroscopically
confirmed Mira variable, which was discovered in 2013 as MASTER-Net Optical
Transient (OT) J212444.87+321738.3 towards the Cygnus constellation. We have
performed long-term optical/near-infrared (NIR) photometric and spectroscopic
observations to characterize the object. From the optical/NIR light curves, we
estimate a variability period of 465 $\pm$ 30 days. The wavelength-dependent
amplitudes of the observed light-curves range from $\Delta$I$\sim$4 mag to
$\Delta$K$\sim$1.5 mag. The (J-K) color-index varies from 1.78 to 2.62 mag over
phases. Interestingly, a phase lag of $\sim$60 days between optical and NIR
light curves is also seen, as in other Miras. Our optical/NIR spectra show
molecular features of TiO, VO, CO, and strong water bands which are a typical
signature of oxygen-rich Mira. We rule out S- or C-type as ZrO bands at 1.03
and 1.06 $\mu$m and $C_2$ band at 1.77 $\mu$m are absent. We estimate the
effective temperature of the object from the SED, and distance and luminosity
from standard Period-Luminosity relations. The optical/NIR spectra display
time-dependent atomic and molecular features (e.g. TiO, NaI, CaI, H$_2$O,CO),
as commonly observed in Miras. Such spectroscopic observations are useful for
studying pulsation variability in Miras.
