Based on the novella. I'm not sure how the movie based on this story went, but I'll assume it's awful.
Not read it? [link]
This strip could have had Twilight and Fluttershy switched roles, but I opted this way for two reasons: Discorded Fluttershy is easier to stop from sacrificing someone than Twilight would be, and evil Angel > evil Spike. That is the most vicious (fake)rodent you've ever seen in your life.