RuneScape/Nightmare Fuel

Spoilers for the game below. Venture past this point only if you dare!

"I'll swallow your soul."
 * The Sea Slug quest line:
 * After you stop Kennith's glowing rage against the poor little girl, he says, with a maniacal portrait box to boot, "Mother Mallum's coming for you!".
 * Where you're talking to the little girl in the same quests, and the zombie-like villagers claw at the house, saying they want to play with her, come outside, etc...pretty friggen' creepy.
 * Pretty much Kennith himself. Kennith can float in a glowing red rage, control the slug infected people, and is probably in cahoots with Mother Mallum, if it wasn't stated in the quest. And he's a kid. A FREAKING KID. His parents are afraid of him. That's pretty nasty.
 * Scary as that was, in the last Sea Slug quest; Kennith grows up and helps kill mother Mallum; and The Hiv-er, the Slugs.
 * "A Soul's Bane":
 * In Tolna's Rift, in the second dungeon, you have to look into dark caves to find monsters. If you don't know whats going to happen, a giant cloaked banshee bounces up in front of the screen. It looks a lot like "The Scream." It's even Lampshaded when the hero screams "AAAAAAAAAAAAH!" the first time. The hero, though, gets more and more confident, until he conquers the fear, and clears the room.
 * That very same rift, at the end of the dungeon, has a deep chasm, with three long necks with heads atop them as the final monsters. It's sort of a situation of Surreal Horror. Those "monsters" at the end are actually Tolna. Not that that makes it any better.
 * The diary of the current owner of the lighthouse in Fremennik Region. It mentions noises from beneath the lighthouse, hearing the waterlogged voice of the previous owner in his dreams, and then he goes to investigate the basement, which is the source of the sounds. There's a reason why the journal ends there. Sweet dreams, dear reader.
 * The faces of Mother Mallum and Lord Drakan the Vampyre. Apparently, they're too hideous for portrait boxes, so they've never been directly seen...and hopefully they won't.
 * Eventually, they're shown in Slug Menace and Lord of Vampyrium.
 * During the Desert Treasure quest, if you have one of the diamonds in your inventory, you could get attacked randomly by a stranger with a poisoned dagger. The worst part is that it can happen anywhere. Even in your own house.
 * The Underground Passage quest. It's a long twisting tunnel, filled with various creatures, a supposed demigod of evil, and every so often you get an ominous message. In order to defeat the demigod and stop the voices, you need to make a voodoo doll of him, and throw that doll down the Well of Damnation, which sends people straight to Zamorak himself. When you do so, he will be sent down the well.
 * Most of the middle of The Branches of Darkmeyer is this, along with large doses of Tear Jerker. During the quest, you:
 * Mock and torture an imprisoned widow, whom you can free after the quest.
 * Kill innocent and ailing prisoners.
 * Drink human blood.
 * Beat a desperate blood tither and then sentence him to death.
 * The dragonkin. To give you an idea of how dangerous they are: Take Lucien. He's got the Staff of Armadyl and the Stone of Jas. The power of Zaros couldn't kill him. And the dragonkin turn up, grab him, impale him on the staff and nothing he does can work against them. Then they show the player a vision of Draynor Village, utterly destroyed, and do the same to Edgeville- and they don't plan to stop.
 * The Boss Banter before fighting Leeuni, where she will gleefully describe crushing the monkey colonist's heads and drinking their intestines, before attempting to do the same to you.
 * Tolna was locked up underground for twenty years. Until he morphed into that... thing.
 * Tormented Demons. Think about it. Their flesh is constantly regenerating and burning at the same time. There's metal sealed over one arm, one leg, and their face. The metal has to be excruciatingly hot. Made worse by the fact that in a letter to a player, the Demons actually seem to be pretty good guys, but apparently whatever magic causes them to be in such excruciating pain also causes them to attack wandering adventurers.
 * Underground Pass:
 * The very disturbing messages that appear in your chatbox during your adventures in the Underground Pass.


 * The quest also features Koftik, who is slowly driven mad the farther you progress through the pass. Luckily, his sanity is eventually cured.
 * "One Piercing Note." A previously-stable woman goes insane, believing herself to be the incarnation of a saint, and starts murdering people. With claws. She kills a totally innocent applicant to the order for no other reason than that she wants to cover her tracks, and ends up mutilating the corpse beyond recognition so people think the corpse is her. She kills another sister for the crime of having an affair, and murderers an innocent novice in front of you for the crime of dancing. Yes, dancing. The ending? She either gets kicked off the tower by the player, throws herself off the tower, or falls off it after thinking she can fly.
 * "Spirit of Summer." The ghosts in this quest look torn and tattered, inhabit a Dark World version of Wilderness ruins, and they can barely communicate with you even with your ghost speak amulet, so there's a sense of wrongness through the whole quest. Finding out what the problem is makes it less scary but also introduces a soul eating Eldritch Abomination to compensate.
 * Three words: Queen Black Dragon. It looks like some sort of Leviathan, is known to be evil, and Jagex noted it that more than ten King Black Dragons can fit into her mouth alone. Made more terrifying how by she used a siren named Remora for unknown reasons, then torched her alive at point blank range. She has obvious connections with the dragonkin based on their symbols being seen often on the way to her. Yes, this Eldritch Abomination is serving the ones that curb-stomped Lucien in an earlier quest.
 * The monster Croesus shows the dangers of greed and pride all too well. Though the Zarosian praetorians were warned that the sentient fungus that they were making into a weapon was growing out of control, they refused to listen. 50 thousand people died, and Zaros himself had to intervene. But though Zaros succeeds in putting an end to the monster, Bik brings him back, and it agrees to be her servant. So now it’s threatening Gielinor itself, as the elder gods wish to destroy the world to hatch their eggs. And he has allies in the form of the Arch-Glacor and Kerapac.
 * The three monsters that Amascut made. They massacred an entire colony of sentient monkeys. And they later did it again. Luckily, the player is given teh option to kill them by choosing to take the Do No Evil quest.
 * The Boss Banter before fighting Leeuni, where she will gleefully describe, before attempting to do the same to you.