The Big Shrink will be the sixth book in the Upside-Down Magic series. Little about it is known.
Little is known about Book #6. However, from the title, it can be presumed that Marigold plays a role. On her 2018 tour, Sarah Mlynowski, one of the authors, was asked about the book by a fan. She describes a new trend, a toy called a greg. The teachers do not allow gregs in the classrooms. Students protest by being shrank by Marigold. The cover has not been revealed, but we can assume it will be like the Sticks & Stones cover.