Mission: Sierra 117
Effect: Dying in single player restarts the entire mission. Dying in coop restarts the last checkpoint - no chance for respawning.
Instructions:When you've rescued Sergeant Johnson at the end of the mission, head towards the hovering Pelican. Do not enter, but instead turn left and run up the walkway's outer right edge. Follow the corners around the building until you reach a shadowy dead end. The skull is yours.