This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Last Broadcast
The narrator of the film is discovered to be the real murderer, kills the one person who knows this and then continues making his film as if nothing has happened
When Locus, after discovering a large amount of Steven's blood, looks up, sees the director, David, approaching them in the dark and turns and runs. It is arguably the scariest moment in the film, and one of the most unexpected.
The disturbing IRC message the crew gets that tells them to look for the Jersey Devil.