Mission: Tsavo Highway
Effect: Enemies always charge, always dive for safety and never flee a fight.
Instructions: Halfway through the level, your Warthog will emerge onto a freeway, the controller will rumble and a Covenant cruiser will fly overhead. Exit the vehicle, jump off the freeway and climb down until you see some support pillars. Leap from pillar to pillar, hugging the left curve of the canyon. You'll eventually find a rocky outcropping with the skull.