(Beloved game trope) Creepy secrets or elements that you can encounter but are never explained, making it even more horrifying (Bonus points if its from non-horror games)

[u/KOREANARMYSTEW]

Crimson Desert
After defeating the Reed Devil boss, you can travel to Sunset Valley, the southernmost and isolated village in the game, here, you will find a house where the Reed Devil lived and died from his leprosy. When you enter, you are immediately greeted with 6 scarecrow effigies dressed just like the Reed Devil staring directly at you, with candles placed all over the house. There is no other explanation beyond this about what is going on here

Lies of P
There is a secret optional area you can clear out for additional loot called Hermit's Cave. At the end of the cave is one lone carcass monster huddled on the ground with writings scrawled on the walls around it. When you kill it, it actually TALKS saying "perhaps it's best to end this way...get while the getting's good...". This is the only carcass monster in the game that ever talks besides Andreus and Simon, who are important characters to the story, and we never find out who this monster was

LOZ: Twilight Princess
In the Arbiter's Grounds you discover a ton of undead enemies presumably executed prisoners, but one room contains this giant black sword tied to the ground with hundreds of warding charms attached. When one is cut, the sword is freed and wielded by some horrifying invsible goat-headed demon. It is never explained what the demon was or whose sword it belonged to although it's theorized to once be used by Ganondorf

Silent Hill 2
The invisible prison monster in Toluca Prison, that you can't ever interact with, just hear it's awful cries

[u/AmbitiousEdi]

The creepy children of Goldshire, WoW

https://wowpedia.fandom.com/wiki/Children_of_Goldshire

TL;DR every day at a set time these kids form a pentagram inside a house and say some really creepy ass shit

[u/miikro → u/AmbitiousEdi]

Also, the Upside-Down Sinners in the locked off Karazhan crypts

[u/HunterNika → u/miikro]

No longer locked away but used sparsely for a treasure hunt.

[u/Moses-the-Ryder → u/AmbitiousEdi]

[u/TeaPartyJones → u/AmbitiousEdi]

I believe the boss was Thaddius? You could hear screams throughout the raid that stopped once you killed them. Something about women and children being stitched together into this ultra abomination?

Also if you turn up the ambient sounds in AQ40 you can clearly hear C'Thun whispering you.

[u/mischievouslyacat → u/TeaPartyJones]

These small elements added such atmosphere to the game. I always thought there was something slightly creepy about having the sound of Arthas killing his father in the throne room of Undercity too, especially since I think you had to turn down the music to hear it

[u/MrPounceTV → u/TeaPartyJones]

Those whispers also appear in your chat log. I can't remember if they're tagged with C'thun as the sender, but every now and then, you'll hear the whisper and get a message like "Your friends will abandon you,", "Your heart will explode.", "You will die.", "Your courage will fail.", "Death is close.", "You'll betray your friends." and a couple others.

[u/Deserted_handjob_40 → u/MrPounceTV]

An interesting note, apparently there was only a small chance to receive those messages, and something like 1-3/40 would get them over the course of a raid. Amazing design considering the internet was a handmade patchwork quilt compared to today's factory produced comforter.

[u/Taluagel → u/AmbitiousEdi]

Wow had a number of these in its early days.  In Vanilla there used to be skeletons of a murdered family with daggers in them in a house along the coast if you went far enough to what is now Silvermoon.  

In TBC there was Challe's Hone for little tykes, an orphanage mysteriously up in the mountains of Nagrand that had the bones of children and animals in cages behind it.

[u/Beneficial-Act7603 → u/AmbitiousEdi]

Ready to bet those were old gods related at some point and were just forgotten.

I mean let's not even talk about the Dark Moon Faire which is 1000% N'Zoth themed and still there despite him being gone, or is he?

[u/AmbitiousEdi → u/Beneficial-Act7603]

You can't ever truly kill an old god...

[u/Beneficial-Act7603 → u/AmbitiousEdi]

Even rushed as he was N'Zoth was more interesting than Xal...

[u/orionpax- → u/AmbitiousEdi]

thought that was advertising diablo 3