This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Fairly English Story
The story is told in first person. Naturally, when the character's mood changes, the narration is affected. So when the main character is overcome with rage or fear, it's pretty damn clear. Especially so for the times he experiences absolute pants-shitting terror or psychotic rage.
When Minato is Charmed by the Lovers, we don't know it at first until he backhands Yukari and calls her a bitch for seemingly no reason. The change is so abrupt yet smooth, and it still feels like Minato even as he beats the ever loving shit out of his teammates.
When Nyaralthotep starts killing his Personas. Alice's pleas for help still haunt some readers today.