The cursed treasure was a conquistador treasure hidden long ago below the site of what is now Crystal Cove. The pieces of the Planispheric Disk were a clue to find it, because the old Spanish explorers used such things as navigation aids and also to mark the location of their hidden treasures.
There was supposed to be a curse associated with this particular treasure, one that has been eating away at Crystal Cove and which could destroy it. Professor Pericles claimed that it was a treasure beyond calculations and that many had died trying to find it.
Inside the crystal sarcophagus was an evil Anunnaki called the Evil Entity that had been behind several of the evil events within Crystal Cove; whenever it spoke, the black pearls inside of the sarcophagus started to rattle. After Scooby-Doo awakened from his nightmare, he warned his friends that the treasure was evil and had to be destroyed.
The treasure, along with the Evil Entity and its minions, was destroyed when it got sucked into a black hole, caused by a team effort of Mystery Incorporated throwing the stick of the Heart of the Jaguar into the crystal sarcophagus.