A series about locked room murder mysteries is expected to be somewhat scary. But sometimes, ''Series/JonathanCreek'' goes that extra mile.
Heavy spoilers below.
* ''The Grinning Man'': The water tank. There are likely several people swearing off baths forever because of that scene.
** The picture of said "Grinning Man" himself is very strong NightmareFuel.
* ''The Three Gamblers'': An evil old man is killed after a drug deal goes wrong. He gets six bullets in the head, and is dumped in the cellar of an abandoned house nearby; they put a wardrobe in front of the door. Terrified that the old guy will still come back for revenge, one of the killers insists on going back to check he hasn't moved... only ''he has'', crawled to the top of the stairs and apparently clawed at the door, despite being very dead. And looking it. He ''was'' dead, but the cellar had flooded, and the body had floated to the top of the stairs, and still looked creepy as hell.
* In the 1998 Christmas special, ''Black Canary'', the backstory involves a magician's assistant who died when some equipment spectacularly malfunctioned and she got sliced in half by a table saw... lengthwise. Gruesome, but it just seems like your run-of-the-mill sort of gruesome--until you really think about the concept of ''lengthwise''. From the bottom up. Maddy sums it up best: "I'm gonna have to sleep with a saucepan between my legs!" Even worse, later there are several flashbacks to this incident, which show that the poor woman was conscious and screaming for ''entirely'' too long.
* ''The Eyes of Tiresias'', a woman is having nightmares about people who are eventually murdered. At first nothing special, just your average ''Jonathan Creek'' episode. Then we get to see one of her dreams, in which a one-eyed man stabs her to death with a sword. Firstly, the amount of blood is really creepy, but then he turns around and has an actually pretty horrible looking mask on. It can really shock you when you're not ready for it.
* The stalker in ''Danse Macabre''. Initially his presence is only mildly unsettling - until [[spoiler:he chops the head off of the corpse of his obsession.]]
* In only the second episode ''Jack in the Box'', it turns out the murderer actually bricked himself up at the crime scene then committed suicide. Meaning that every single time Jonathan and Maddy investigate the murder scene for clues ''there was an unseen dead body right behind the wall''.