Thanks to all who made suggestions for the tag line for Troll Valley.
Although I had decided to go with something else, I thought it over and concluded that commenter Adam had the best suggestion. His tag line will go on the book, in a slightly modified form:
“The Fairy Tale Your Grandparents Never Told You.”
Adam will receive a free copy of Troll Valley once the thing is published. Assuming he has the capability to download e-books.