The Proton Gunner is a gunner station that shoots particle streams. It was conjured by Winston Zeddemore in a dream.
After being reunited with the other Ghostbusters in a sleep state, Winston materialized the Proton Gunner and a helmet to take out the Mean Green Teen Machine. All it's streams did was blow up Guggenheim's pizza. He retaliated by dreching Winston and the gunner with pizzas.