This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Pages Of Harmony
Just about everything that Twilight does is this.
The various death sequences,To summarize each of them is quite graphic and violent and are all described in extensive detail.
Its not just the way Twilight kills her friends, its the fact that each method to extract each element is ironicly tied to her friends personality, and then there is the realization near the end that in order to gain the final element she would need to completely destroy herself.