It's interesting to see what the artists can do with such a broad theme. Emily Carroll's "Under the Floorboards" is reminiscent of Anya's Ghost and Jason Caffoe's "The Keeper's Treasure" has beautiful illustrations and a great message. My favorite story might have been Rad Sechrist's "The Butter Thief", where a Japanese grandmother uses a box to protect the family's butter from spirits who want to steal it. Charmed by its unusual plot and cinematic artwork, Sechrist is an artist I will be watching. Kibuishi himself contributed the final story, "The Escape Option". Fans of the Amulet series will be eager to see more of his unique imagination and gorgeous art.
Explorer: The Mystery Boxes is fairly slim at 128 pages, and most stories could have benefited from a few extra pages. I will be adding it to my classroom library, where it will probably never see any "shelf time". If you enjoy the Flight anthologies, you will love this book.