You only actually need 6 of the 17 skulls to solve the puzzle. The ones you need are:
The Easter Island Skull on the right of the Skull Chamber.
The Mayan Skull from the El Castillo Inner Chamber.
The Atlantis Skull from the room leading to the Xtoloc Cenote.
The Stonehenge Skull from the Sacrifical Chamber
The Giza Skull from the Sacred Ceynote.
The Devil's Triangle Skull from the sacophagus in the Statue Chamber.
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