Twilight Sparkle had been looking forward to a quiet, relaxing day with a friend, but when Twilight discovers Fluttershy's appetite for blood, the knowledge proves to be anything but relaxing...
Trixie's line of work is dangerous. But she's a careful showpony, and that's why she's only died a few dozen times in her career. She thinks this is normal.
An ancient magical artifact causes floating lie meters to appear above everypony's heads. This causes Twilight to reflect on honesty and friendship. Based on an idea by theworstwriter.
When Twilight accepts Cheerilee's request for her to substitute teach, she quickly realizes the topic is "the birds and the bees". So, not wanting to let down her students, Twilight attempts to teach the subject to the best of her ability.
The princesses gave their magic to Twilight to prevent Tirek from stealing it. As a result, they end up stuck in Tartarus. The fact that things manage to go downhill here says a lot about the wonders of family.