Grossjuck Industries' Robo-Buster was tasked with eliminating all paranormal threats in New York. Its proton technology claimed to destroy non-corporeal entities, violating a basic rule of ectoplasmic physics. In reality, all of the ghosts "destroyed" by it were shifted into the space-time continuum. As a result, an enormous kinetic energy buildup led to flux in the etheric continuum. Eventually, the continuum reached critical mass and one humongous ghost manifested from the essence of all these "destroyed" ghosts. Egon Spengler picked up an unusually high reading on the P.K.E. Meter and detoured Ecto-1 eastward, instead of confronting Paul Smart, President of Grossjuck Industries.
Robo-Buster "destroyed" the giant mass after its initial manifestation above a park but it later appeared at Grossjuck Plaza. The mass wanted revenge on Paul Smart, the one who unleashed the Robo-Buster on them. It tried to zap at the creature, but it kept on reforming after parts of it were destroyed. One of the ghosts then possessed Robo-Buster but was exorcised by the Ghostbusters. They eventually defeated the Giant Mass Ghost by laying out several traps and catching all of the ghosts that made up the huge phantom. Robo-Buster also helped after Egon adjusted his proton cannon arms to work like regular proton guns. Peter Venkman managed to wrangle Slimer free during the battle. About 10 traps were used in total to completely capture the mass.