Entry location: Level: Outskirts
Words on screen: "I would have been your Daddy"
Effect:Apparently, this skull unlocks all sorts of interesting dialogue. Check out this link for more information.
How to get to the skull: The specifics of this skull are still a bit sketchy. The best thing to do is watch the videos showing how to spawn the skull and just keep trying until you get it to spawn. The main thing appears to be getting the checkpoint right past the pelican that picks up Johnson. This checkpoint spawns the sniper jackals in 'sniper alley.' The skull itself is in a room on a balcony. The room contains a sniper rifle and sniper ammo, and if you're one of the lucky ones who can get the skull to spawn, it will also contain the skull. Picking up the skull teleports you to the ground level, and gives you just a Plasma Pistol. You will quickly be assaulted by Elites. Some people say that grunts and jackals will also spawn, but I've never seen them do so. In my video, 7 waves (not 6, like I said initially) of Spec Op Elites come out. Killing the last Elite will have the text for the skull flash, meaning that you have to kill all of the Elites to actually finish getting the skull. If you die to the Elites, and your checkpoint no longer spawns the skull, kill yourself 4 or 5 times to be pushed back one extra checkpoint. The skull should spawn for you again, so you can try the fight again.