kill the anti-air wraith, , wen it says destroy all wraiths, drive the warthog down to the second building close to the rock wall there is a circle building that you pull the warthog up to the side of it, and get out and jump on the warthog then jump on the building. that is for catch skiull...
Fog skull:
go to the level floodgate, as u walk toward the town, u will see a road look at the top of the right building, make sure u have ur BR scope on pointing up on the roof of the building, and u will see a flood guy running to jjump across the road and . u have to shoot him in the head before he does. and the skull will drop to the road