In $\mathrm{AgF}_2$ oxidation state of Ag is +2 which is very unstable. Therefore, it quickly, accepts an electron to form the more stable +1 oxidation state. $\mathrm{Ag}^{2+} + e^{-}$ → $\mathrm{Ag}^{+}$ Therefore, $\mathrm{AgF}_2$, if formed, will act as a strong oxidising agent.