Under what conditions does MnO2 acts as an oxidizing agent? It's very strong in acidic medium. Does it have low or nil oxidizing ability in neutral and basic media?

Does heating solid $\ce{MnO2}$ give it better oxidizing properties?
It certainly is  powerful oxidizer when heated! Thermite can be made with powdered aluminum and $\ce{MnO2}$, and is at least as spectacular as with $\ce{Fe2O3}$ as the oxidant.