Through sheer bad luck, Twilight and some friends are stuck, and they cannot get out. What stuck them, and made them stick, stuck where they are, is a thing that sticks things into places that they become stuck in. To speak in more precise tones, it's a librarian. It just so happens that old and forgotten mythological creatures still exist in Equestria and elsewhere, and it's the luck of the draw as to whether you will run into a good one or a bad one on your journeys through Equestria, or other countries, with similar creatures and histories.

This is a bad one.