All four Ghostbusters are sliding towards the camera; just after Egon slides out of frame, Peter suddenly becomes Egon (the animators miscolored Peter's hair and jumpsuit using Egon's color palette).
When the Ghostbusters are shooting at the killer tube of toothpaste, Winston is colored exactly like Ray. The order they're standing in also changes between shots.
When Slimer is eating the ping pong ball, the fire station ceiling is not visible, but it is in all the following shots.
When Winston is prying Peter off the wall with a chair, the outline of the door in the background is visible through Winston's hair.
After the Ghostbusters enter the ghost Television tower, Egon (shown only from the waist down) is wearing the same color jumpsuit as Ray in one shot.
Just before Winston decides to throw the 'six-pack' he is shown in the background, while another Ghostbuster's legs walk into frame in the foreground wearing the same color jumpsuit as Winston.