Charmonia decays provide a clean method to study properties of light mesons. In particular with 6.7$\times10^6$ $\eta'$ mesons from the radiative $J/\psi$ decay, BESIII is the world leading facility for $\eta'$ decay studies. For many $\eta^\prime$ decay channels the low background data samples are up to three orders of magnitude larger than collected in any previous experiment. The analyses range from detailed studies of the common decays dynamics, observations of new radiative and Dalitz decays with branching fractions ${\cal B}\sim10^{-4}$ and search for rare/forbidden decays with sensitivity up to ${\cal B}\sim 10^{-5}$. The most recent results include precision studies of $\eta'\to\pi^+\pi^-\gamma$, $\eta'\to 3\pi$ and $\eta'\to \eta\pi\pi$ dynamics. The highlights include observation of $\rho^0-\omega$ interference and the need of a contribution beyond pion form factor in $\eta'\to\pi^+\pi^-\gamma$ and $\eta'\to \rho^\pm\pi^\mp$ contribution in $\eta'\to \pi^+\pi^-\pi^0$.