In the final battle with main antagonist, the villain suddenly vanishes and a disembodied voice demands of the cast to choose the form of their "destructor." The ghost-busting team attempts to clear their mind but a thought pops in to the head of Dan Ackroyd's character Ray Stantz. He explains that he, "tried to think of the most harmless thing." But just then, a giant Mr. Stay -Puft Marshmallow man is seen walking towards them.
They defeat the destructor marshmallow by 'crossing the streams' of their proton packs shooting into the portal. The resulting explosion destroys the marshmallow man and coats the city and cast in marshmallow.
Not yet the Ghostbusters, professors Venkman, Stantz and Spengler encounter a ghost resembling a librarian after being asked to investigate disturbances at the New York Public Library.
Following their encounter with the ghost, the team returns to the university to find their research grant has been terminated and the dean orders them to vacate the university. Following this termination, the team decides to go into business for themselves and form the Ghostbusters.
The ghostbusters arrive at the fictitious Sedgewick hotel to learn about a disturbance on the 12th floor. The hotel manager shares the 12th floor is known by staff to have a history of disturbances but on this night the disturbances have become too much to bear. The ghost they've been called to handle is first encountered on the 12th floor but ultimately captures in the ballroom on the 1st floor after considerable damage is done to the ballroom.
While the Sedgewick may not be a real hotel, the actual hotel where the scene was filmed is recognizable as the Millennium Biltmore in Los Angeles.
While the iconic scene shows Peter Venkman opposite a charging ghost, referred to as the slimer, its Dan Aykroyd's Ray Stantz who describes the ghost as an "ugly little spud" over the radio.
The encounter leaves Venkman on his back and covered in slime.