Interesting and fun scenario. I skirted the rules, potentially, in a couple of ways and still nearly lost.

1. I played with 5 ghostbusters (the original 4 from the first game - GB1) as well as Slimer from the expansion of GB2)
2. The first two campaigns, I didn't play with the goo timer. I did play Scenario #3 and #4 with the timer.
3. For Random events or missing the Big Plazm from Scenario IV, I brought in the relevant ghost class from GB1 (Ghalloping Ghouls)

It came down to the last turn. Ray was close to the painting so Vigo pulled his drained soul. Peter had gotten Vigo on the painting with 1 stream.

Ray's turn, he fired at the drained soul and missed so the drained soul moved next to the painting. I choose not to fire again with Ray at the Drained Soul as a miss would lose the game.

Eagon's turn, he went after Vigo on the painting and fired with success. I won the game by one turn.

The GB2 versions of the Ghostbusters are trash. Play Peter, Eagon, Ray, and Winston from GB1. I have had a lot more success. Slimer's ability to go through non-passable spaces is invaluable. It was actually the only power of his that I really utilized.

You can't win GB2 without a little luck. If you start missing rolls, you get in trouble fast. This is why you really need the Ghostbusters from GB1 to win.