There's a sequence in the episode "Statue of Liberty" in which: The Ghostbusters go up a reeeeeally long flight of stairs (sound familiar?) in pursuit of Mysteria. Mysteria catches up to Eddie and surrounds him with mist. Eddie falls, and Tracy uses the Ghost Gummer to catch him in the nick of time! The sequence was reused in a later episode, replacing Mysteria with a generic orange ghost!
Referenced by...: The Funday Pawpet Show: In this clip at about 10:05, the opening credits run as Poink explains the series to Yappy. Oddly enough the music is the Ray Parker Jr movie/Real Ghostbusters theme...and it fits in with the animation like a glove.
In the original "series bible" (the document which lays out the vision of the series), the moronic Airhead was described as working for the Ghostbusters while serving Prime Evil—in other words, a mole. This gave his incompetence a very interesting angle, but in the finished series, he was just a moron.
In her original design, Futura was an African-American with long, light-brown hair, and Jessica Wray originally had blonde hair.
Prime Evil was originally designed to resemble Mumm-Ra, while Scared Stiff was originally conceived as more of a "walking fridge" robot and Mysteria originally had a human appearance and a long red dress.
Tex-Hex from Bravestarr was originally meant to be a Ghostbusters villain. Lou Scheimer took one look at his character-sketch and decided that he should be a Big Bad in his own right.
Most likely the animators were told to time the intro animation to the Ray Parker Jr music just in case a last minute agreement with Columbia Pictures (or case handed down in court) allowed them to use it.