the whole concept of gb3 is like any sequal idea, and that is that it will usually not work good. we've all seen sequals of movies, and we've all noted that the sequals usually suck. gb2 was on of the exceptions (so was the empire strkes back and attack of the clones, if you're into that kinda thing). anyway, plot idea. my friend subway_ghost has a good concept going for it. at this point, you'd most likely need new ghostbusters due to plenty of reasons. i hope everyone has talked about and agrees that they need to cast unknowns for the parts. but you can't really reuse and rescrap old ideas, like using gozer and vigo in the third. but you'd probably need gozer coming back to open the gates for a new evil spirit, although the devil isn't really a good idea due to the fact that all those christian people would be meanies about it. ghostbusters has slightly been biblical, and if you read the bible, you realize that cain, the first murderer, is going to take over hell in the end, right? well, this could take place after the uprising of cain. the spawn of gozer, which would reside in oscar, would come out and release havoc on the world, much as said above, as a way to signify that hell has a new ruler, and opens the gateways for cain to come back (ugh, now it reminds me of robocop2, a really bad sequal). i'm not providing this information as a plot, merely an add on plot to the other two above. they just can't do anything stupid though, like bring back stay puft, and slimer should be meaner like in the original. louis should also be a ghostbuster, you know, because of his high ambition in gb2. it wouldn't make it dumb, i don't think. also, the plot shouldn't start out like gb2, where they were sued like a son of a felt tip pen. unemployment perhaps? after all, you remove all spirits, you remove any job. i'd say the havoc should be released all over the world, but that'd get too confusing.
also, dude up above who's name i forgot, how come you can't remember any names of anybody from the movie?
taxi ghost was the ghost who was a taxi driver in the first movie.
i'm new, by the way