Dyson Brownian motion, the eigenvalues of matrix-valued Brownian motion, has become the most standard and well-established approach to universalities for local (i.e. microscopic) eigenvalue statistics of Hermitian random matrices. When combined with a noble characteristic flow method, it can also help study the eigenvalue statistics on a mesoscopic scale. In this talk, we demonstrate this mechanism via yet another simplification of the proof of local laws for Wigner matrices and discuss some generalities.