The Crystal Cove treasure with a (arcophagus.
Nibiru is a legend well-known in Babylonian history.
Legend of Nibiru
It tells the story of how a large object, either a planet known as Twelfth Planet, Planet X or Nibiru, will collide with Earth. It is referenced as "The Doomsday Event". In this event, god-like creatures on the planet Nibiru will arrive on Earth. One known sentient of the planet was captured inside a sarcophagus. A planispheric disk was created in order to make the treasure hard to find, first created by the Conquistadors who realised the power of the god inside. They then went their seperate ways, with the pieces of the disks which were eventually found by Mystery Inc. It turns out that Nibiru is an evil Anunnaki that was sealed in a sarcophagus in the the treasure beneath Crysal Cove.
History
Scooby-Doo! Mystery Incorporated
Season two
"Nibiru" spoke through the ghost of El Aguirre, leader of the Conquistadors as Mystery Incorporated left Mount Diabla. (Night on Haunted Mountain)
Abigail Gluck said it when Mystery Incorporated found her corpse. (The Midnight Zone)
Velma Dinkley searched on her website for any information on Nibiru and discovered it to be the doomsday event. Unknown by Mystery Incorporated, after they connected the Planispheric Disk together, the sarcophagus in the lost underground city uttered the word "Nibiru". (Wrath of the Krampus)
Velma cobbled together a player for the Planispheric Disk, and it produced the word "Nibiru" also.
After solving a mystery, the real mummy Friar Serra returned to warn them of "Nibiru", a cataclysm that is inevitable unless "the dog dies". (Theater of Doom)
An Anunnaki possesses Nova and appears in Scooby-Doo's latest nightmare telling him that Nibiru is coming. She tells Scooby-Doo to destroy the cursed treasure before the evil Anunnaki is released. (Stand and Deliver)