His original 80 page treatment involved people doing ghostbusting in the future where teams would compete, however, Reitman wanted to do a going into business story, due to the fact that Dan's original treatment would be too expensive to achieve.
When auditioning, Sigourney wanted her character to be possessed and started acting like a dog.
John Candy was offered the role of Louis and he wanted his character to be German and have German shepherds.
William Atherton to this day still gets called "Dickless" thanks to Bill Murray improvising the line.
The actress playing the maid had no idea of how effective the sparks would be when the trolley gets blasted. Her "What the hell are you doing?" was ad-libbed.
Atherton was to covered in 100 pounds of whipped cream, but after testing it on a stuntman, which knocked him out, it was suggested to 75 pounds.
We also get interviews with the VFX team and also how Slimer and the Library ghost were created.
Also, we have pop up trivia for the characters, the ghosts and the gadgets.
Overall, a fun feature and a nice retrospective. But it's a shame that Bill Murray and Rick Moranis were absent. The former dislikes interviews, and the latter left show biz.