House on Haunted Hill (1999)

Revealing mistake: When the house has been locked down at the beginning of the film no moonlight could come in, however when the guests are being shown the coffin with the guns in there is a shaft of bright moonlight shining on to it.

Deliberate mistake: When Eddie and "Jennifer" are walking around the house alone, she is trying to tell Eddie that she's really Sara. But by the time she is explaining that, Eddie has disappeared. She doesn't find him until later. But from the moment she finds him (and he is talking to her) he calls her Sara, despite never actually hearing her say that. Also, after they all get back together, a few of the other people start calling her Sara as well, but no one actually heard that either.

Factual error: In the scene where the cast find the guns in the tiny coffins, they mention that it is not possible to tell if they are loaded because the clips are welded. Being semi-automatic pistols, simply pulling back the slide & ejecting the first round would have easily determined whether live or blank rounds had been loaded.

Trivia: The Terror Incognita roller coaster is actually The Hulk roller coaster in Universal Studios, Orlando.

Trivia: The darkness that emerges and begins to kill the guests was actually created when the animators took film of dancing naked women and mirrored the image over and over.

Trivia: If you wait until after the credits roll, you get to see what happens to the souls of the people who died that night - i.e. Evelyn and Steven.

Melissa Marr: Now, that's enter-fucking-tainment.

Evelyn: You know if you really love me, you'll find a way to drop dead in the next three seconds.
Stephen Price: Finding ways for me to die is really your deal, isn't it Eveline? Let's not forget the OJ knife with the not-quite-retractable blade. Your Jim Jones Kool-Aid was exactly that.
Evelyn: Accidents, all accidents until proven otherwise.

Peter Graves: Dr. Richard Benjamin Vannacutt. He out-butchered Bundy, made Manson look meek.

Question: What happened to the carriage on the rollercoaster that flew off the rails?

Question: Eddie reveals that he's not even a direct descendant of the original staff but was actually adopted. Why would the Darkness still try to kill Eddie even though he had no ties to the staff or institute?

Question: Who exactly is the person that Melissa sees behind her before it attacks her?