There's something strange in the neighborhood, but it's not a sequel.
The good news is that it does happen to be a pretty humorous homage to the original Ghostbusters film performed by a troupe of
Of course, while the Library had knowledge of the stunt beforehand, the guard you see in the footage did not. Between you and me I'd be a little nervous watching these "ghosts" make their way in one-by-one. Luckily, its not too long afterwards that the Ghostbusters appear (or at least agents in Ghostbusters attire and inflatable proton packs) and proceed to chase the spooks back where they belong. It's great to see the "audience's" reactions as some people are bowling over laughing while others are completely clueless.
If you're interested in more of a behind-the-scenes play by play, check out Improv Everywhere's official Mission Page.