Reminds me of a story I read just a couple weeks ago.
Princess Celestia has serious issues over having banished Luna, and after Twilight gets alicorn'd she brings her in for some special training--training to teach her to withstand anything for the sake of Equestria. This consisted of her using dark magic to murder Twilight in dozens of different ways, healing her from the brink of death each time so they could keep going (ignoring the screaming, the begging, the pleading, etc). After a while, Twilight couldn't do anything more than just lie there and be gutted, so Celestia decided that was enough for the night, and let her be so they could pick up the next day.
Twilight ends up going into her dream (and quite disturbingly, Celestia doesn't seem to have noticed that Twilight had a problem with what she had done to her at all, and seems completely surprised that Twilight was upset at all. It's mentioned that she's projecting her self-hate into "teaching" Twilight) and killed her in her sleep. Knowing that she'd spend the next aeon carrying the same guilt Celestia did for banishing Luna. She went sort of insane.
Darker than what normally interests me, but the story fits this art spectacularly.
Celestia: "You will not turn my battlefield into a library." "Now hear this Twilight Sparkle, you are not wanted upon my beloved battlefield!" "I will send my condolences to your parents." "You are a coward, and you've died like one." "If you want to fight a mare, look her in the eyes." "Shining Armor did not prepare you for the level of violence you will meet on my battlefield!"