This was the pilot episode before Ghosts R' Us.
The Doomsday Door had Sumerian writing on it and was supposed to be used after the world was destroyed. Gozer, the villain from the first "Ghostbusters" movie, was a Sumerian god who was supposed to destroy the world. Both manifested in New York City.
Ray Stantz reveals that he has season tickets to the New York Mets. In the first draft of the script, it was supposed to be the Yankees.
A sewer cover reads "AJIA-DO," the name of the Japanese animation company.
The voice actors were recorded on June 23, 1986.