The Sun Gun is a type of Plumber weapon that projects a beam as bright as sunlight.
It has a broad white handle to hold it with a blue button to activate it. The part from where the beam is projected has a shade of light blue.
One version of the Sun Gun appeared in Ghostfreaked Out. It was of Plumber design, and was used by Max to repel Zs'Skayr.
Another version appeared in Be Afraid of the Dark. It was created by Grey Matter using scraps of machinery, and served the same purpose as the previous version and was also used to repel the ghost.