This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Neverwinter Nights
In Chapter 3, you can find a Cultist's journal describing the execution of a traitor. The journal recounts one of their number was quiet as they walked one day and then suddenly asked if they were really doing the right thing. The leader had her stripped and tied between two trees, and whipped her until flesh hung from her back. She cried out for forgiveness and he was considering letting her live, until she begged for Illmater to help her. The leader then cut out her heart and burned it as a sacrifice.
Klauth, the red dragon. He's powerful enough to intimidate an entire tribe of fire giants into serving him.
The Charwood. Do not adventure in this region shortly before bedtime. We mean it. It becomes more of a Tear Jerker once you find out the backstory, but it's still pretty scary.
In Shadows of Undrentide, there's an archaeological site on the Netherese you have to travel to to discover the true purpose of the tower crystal. When you arrive, the entire team is dead aside from one person who conveniently dies right after he vaguely warns you about the person who attacked the camp. Upon entering the temple, you're treated to the sounds of dozens of flies in your ears and several corpses. Throughout the entire temple, there are suits of armor around the Temple,most of which do nothing, but some attack you.