This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Sword of Truth
One of the earlier Sword of Truth books has this thing toward the end with rats eating someone alive. To be more specific, the villain of the book has tied down one of the hero's allies, put a rat under a bucket on her stomach, and starts heating the bucket. He deliberately chose this torture because the victim had an earlier established fear of rats.
Rather chillingly, almost this exact scenario happened in 1984. It also appeared in George Fielding Eliot's The Copper Bowl, Nightmare Fuel in itself, which dates from 1928.
In "Blood of the Fold" we get introduced to Emperor Jagang, a Dream Walker whose magic abilities allow him to slip into the cracks of a wizard's thoughts and control them completely. He then proceeds to kill one of the Sisters of the Dark in front of the others, and then uses his power to show them the extent of what their punishment in the Underworld will be if they displease him and die. At first the dark sisters think Jagang is torturing the victim. When asked how long he will keep this up before letting her die, he calmly explains that she was dead before she hit the floor. He lets them watch their comrade's thrashing, screaming corpse, all the while while rendering them immobile and while chowing down on some turkey. When they ask how long she will scream, he answers, "Until she rots." And then, he orders her corpse to be thrown into the privy pit.
The chimes...the fricking chimes. Don't say their names out loud.
The two young graduates of the Wizarding School who have been lifelong friends and nominally in service to the Light, only to be told by the Big Bad that one of them has to be flayed alive, whereas the other has to join the Dark Side and perform the flaying as part of his initiation. And one of them did it.
Chickens aside, the idea that the Chimes of Death can just suddenly show up and make you drown yourself can be frightening.
Creation of Mord-Sith. It involves choosing the nicest girls, and breaking them. How? It's done THREE times. First, she has to get used to pain. Second, you have to make your father your slave and torture him to death. Third, you must do the same to your mother. Fortunately Richard abandoned this practise, and all Mord-Sith respected him so much that they continued to serve him.