Also, the guy whose body gets folded like a piece of paper. You see his bones break in 90 degree angles on screen!
In "Lockdown", with the plague that makes people's veins turn black before they bleed out of every orifice and die.
In "The Farmer", with the various organ thefts.
In "Over My Head", with the girl who gets killed by an invisible shark in a swimming pool, the guy who drowns on land (this also happens to Duke, but Audrey saves him), and the guy who gets swarmed by hundreds of tiny crabs.
In "Double Jeopardy", the various punishments Lady Justice doles out.
The Skinwalker - most people run afoul of their Troubles on accident, through trauma or stress doing something they do everyday. How the hell do you find out that if you wear a person's skin you can become them? It's even more disturbing if they had one of the few Troubled families who taught them about their Trouble.
How you ask? Having your skin melt off is a good start. Troubles are also shown to have an instinct attached to them, driving the person into a situation where they would be used. The same is true here.
In "Bad Blood", a man's blood goes around killing people. With one touch, it can completely drain you of your blood, getting bigger and bigger with each victim. It started out as a few drops.
Jordan's death in "Countdown" is disturbingly drawn-out and painful as Wade guts her and restrains her until she bleeds out. No one deserved that.
In "The Trouble With Troubles", a freaking volcano appeared in Haven on account of The Troubles.
In "When The Bough Breaks", whenever a baby cries, a random (and I emphasize, COMPLETELY RANDOM) person in town dies.
So many things in this episode is pure unadulterated Nightmare Fuel. An entire family whose male members are taught never to cry. The story of a mentally-challenged cousin who they weren't able to teach, and what they had to do to him. The fact that enough people once died of this Trouble that it was successfully covered up as an outbreak of the Spanish Flu. The fact that there seems to be no way to fix this other than killing the baby or giving Duke back the Crocker family Trouble and having him kill the baby's father.
"The Lighthouse:" the evil, evil smile that appears on Audrey's face when Mara's personality awakens. Chilling.
"See No Evil" is full of Nightmare Fuel. A few examples:
The Trouble Of The Week, which causes people's eyes and/or mouths to spontaneously sew themselves shut. According to Dwight, it is surgically impossible to remove the stitches. And further, it's implied that this Trouble was one of the ones the Crocker family already wiped out, and it's back because Duke's Trouble is out of control, and anyone who might tell him Jennifer is dead becomes a victim. And with Audrey not available, no one has any clue how to stop it. For further Nightmare Fuel, just think of the Troubles we know Duke has. Hint: eating organs and making people die by crying. Yeah, he's a walking amalgam of total horror just waiting for a trigger.
Mara is actually very, very scary. She's utterly ruthless, she knows how everyone's Trouble works and how to exploit them, and because she has access to Audrey's memories, she knows exactly what buttons to push to drive a wedge between our heroes. The fact that all this evil is coming out of the form of the Audrey Parker we've come to know and love just makes it worse.