Näcken's music taking control of Olle's body and forcing him to dance uncontrollably as he's pulled closer to the creature.
The Swamplands:
The premise is that Olle is out to save a baby from being ritualistically sacrificed by a witch. He doesn't succeed, finding the "midwife" having hung herself after drowning the poor infant. Olle takes the time to bury it so that it doesn't become one of hundreds of lost souls in the marshes.
Everything about Kärrhäxan is unsettling. When you first encounter it, you confuse it for a scarecrow, only for a cutscene to go off and show that the scarecrow is alive, with a closeup of its face — an animal skull covering a vaguely humanish face and glowing silver-eyes — and you have to walk away hoping it doesn't attack you then and there. You spend the rest of the marshland level looking over your shoulder, convinced that it'll attack you out of nowhere until you finally encounter it as you try to cross a stretch of water, having somehow found its way there while still limply hanging from its post.
The destroyed village filled with literal zombies.
The backstories of human wickedness can be pretty alarming too, from King Nils's Witch Hunt to Näcken's abuse (for what?) by his peers to the innocent young prince's assassination to the dead village's mass lynching of women for the "crime" of looking a bit like the Skogsrå's human guise.
