Blair Witch was a one time lightning sort of experience, I am sure most didn't expect it do well.

That can be said for a lot of blockbusters that get sequels though.

That's why Prince Caspian is a great example. Potter, Twilight, Hunger Games, they all had relatively small decreases or bumps with their sequels, and I think most expectations for the more action packed summer released sequel to do at least 250 million in the states. I don't think anyone would ever have predicted that Sex and the City would have done better than the first Narnia sequel.

Exorcist II is has one of the worst film trailers ever, and while it was a footnote comparison to the original, it was a small hit for the day. That can be said for a lot of 70s sequels. I think of something like French Connection 2 which no one remembers, but it's a really good followup and one of the better sequels ever produced. Using that thinking, one could argue The Godfather Part II. Not even a third of the first films gross despite equal praise, 2 years in between films, etc. Granted I'm talking about re releases (Not sure what the first made in it's original run)

I wonder how the Godfather Part II would have fared in modern setting. I think it would have been a lock for 100+ opening.

It's still Prince Caspian for me. Still can't believe how badly they fumbled it, to the point where they abandoned the franchise. It could've been a mini Harry Potter for Disney if they had played their cards right.