One of the more unexpected joys of Disney’s Frozen 2, which would go on to become the highest grossing animated feature of all time, was how well it deepened and expanded the mythology and mystery of the Frozen world. But a new book looks to explore those mysteries more fully. Ahead of this weekend’s virtual edition of Frozen Fan Fest (which will include, amongst other things, a trailer for the upcoming Olaf-centered short film “Once Upon a Snowman”), we are so thrilled to bring an exclusive excerpt from Frozen 2: Dangerous Secrets: The Story of Iduna and …