Wow this is an old topic. Figured it would have still been pinned.
Oh well. This is where the guide links to.
For the above poster, youre probably just not on the top platform. That was my problem.
Now for the real reason Im here: a couple fixes and some new info.
First, the Multiplayer Armor page is seriously messed up. The text and images are really out of line. The Achievement section needs to be tweaked as well.
Second, for the IWHBYD skull, you dont have to go through that big sequence of rings. Instead, you can do the following order: 4 6 5 4 5 3 4
Thats how I got it, so I can verify it works.
Finally, for the Famine skull, since I cant grenade jump, I found a new way of getting up there. You need two ghosts and a deployable cover.
While under the bridge, drive the ghosts around the corner towards your next objective. Straight ahead you should see a pile of rocks (one large rock and one smaller one) right in the middle of the path. Drive up to the and turn about. You should notice that the wall on the left side is kind of a slop. Use your boosters to ride up the wall at an angle towards the walkway, and, without stopping, you should be able to launch off the top of the cliff and onto the walkway. Pilot the ghosts over to the last pillar where the skull is. Park one on the slop beside said pillar (get out of the ghost quickly or else it will slide off!) then park the other ghost on top of it. Stand on the slop behind the ghosts and throw your deployable cover on top of them as close to the pillar as you can get it. Now its fairly easy to jump on top of the cover and onto the ledge with the skull.