1.) You might continue with the story of the GB2. The painting of Lord Vigo came to the museum for restavration, right? So where did it come from? The guy had a castle. And remember that he was not destroyed, his painting nearly changed into another painting of some very cool guys
. So Vigo can either be in some other painting, or could return to his castle (then you could have the film in East Europe). If he just jumped into another painting, he might be everywhere. Even hanging on a wall of an evil rich Satan worshiper.2.) You might pick up from the story of the original movie. Remember that there were Gozer worshipers at the turn of the 20th century. The architect who build the skyscraper was one of them. They are still around and could be into some wierd cult things. Calling ghosts, gods of the other side etc. And they could be getting their knowlage from books bought at Ray's Ocults (remember his little shop form GB2). He might even try to join them, ‘cos he’d suspect something. The rest of the guys eould try to find him.
3.) Then there's Oscar. He should be in puberty by now. Have you seen the Exorcist. A demon might try to posses Oscar. By the way Vigo was holding him and tried to merge with him.
4.) Or you can just find something new. there are old Burial Site of Native Americans that have not been treated too kindly over the centuries and there spirits wish to punish the people for not worshiping them
, or you might include the Titanic - it arrived to New York in 1989 .There are just so many possibilities. I know I'm new to this site, but I've been a Ghostbuster fan ever since the 6th of February 1987 and I want more of the great ghostly stuff.