Book of Ruins
From the Super Mario Wiki
The Book of Ruins is an item found exclusively in Mario & Luigi: Dream Team, and the fifth item collected during a series of item trades pertaining to a sidequest in Wakeport. It is apparently a rare book that usually only ruins researchers receive. Mario and Luigi are given this item from a Brock who is a big fan of Princess Peach in the panel puzzle to the west of Pi'illoper's house after they give him Peach's Photo.