"A mysterious skull carved out of crystal. Of high artistic value, this find is unique...and a little spooky."
The Crystal Skull is a one-time, unique salvage item that the player can find using the clues from the treasure request titled "Cursed Rumor" in their notebook. In order for this request to be activated, the player must first complete the map of the Cortica River Midstream, which requires that the player befriend one specific Amazon River Dolphin in order to unblock a barricaded section of the river. After that, the player should be able to find the Skull in the Mangrove Maze area, but only in the nighttime.
The appraisal reward for finding this item is ten thousand pelagos.