  We present new spectroscopic observations of Ly$\alpha$ Blob 2 (LAB2) in the
SSA22 protocluster region ($z \sim$ 3.1). By creating a narrow-band Ly$\alpha$
image, we observed extended Ly$\alpha$ emission in three distinct regions, in
which the highest Ly$\alpha$ surface brightness (SB) center is far away from
the known continuum sources. We have searched through the MOSFIRE slits that
cover the high Ly$\alpha$ SB regions, but are unable to detect any significant
nebular emission near the highest SB center. We further map the blue-to-red
flux ratio and find that it is anti-correlated with Ly$\alpha$ SB with a
power-law index of $\sim$ -0.4. To decode the spatially-resolved Ly$\alpha$
profiles using Monte-Carlo radiative transfer (MCRT) modelling, we use both
multiphase, clumpy models and shell models and successfully reproduced the
diverse Ly$\alpha$ morphologies with reasonable physical parameters.
Significant correlations exist between parameters of two different models, and
our multiphase, clumpy model parameters naturally alleviated the previously
reported discrepancies between the shell model parameters and data. In
addition, we have modeled Ly$\alpha$ spectra at different spatial positions
simultaneously, and we find that the variation of the inferred clump outflow
velocity can be approximately explained by line-of-sight projection effects.
Our results support the `central powering + scattering' scenario, i.e. the
Ly$\alpha$ photons are generated by a central powering source and then scatter
with outflowing, multiphase HI gas while propagating outwards. The infalling of
cool gas near the blob outskirts shapes the observed blue-dominated Ly$\alpha$
profiles, but its energy contribution is likely to be minor compared to the
photo-ionization by star-forming galaxies and/or AGNs.
