Every time I go to the location it is never their. walkthroughs say that it should remain on the silo in the middle of the lake bed until the regular wraith is destroyed.
it does, just got it the other day. It's a Legendary skull though, so if you're not on legendary it won't be there.
It has to be on normal+, not only legendary^, and it's not the silo in the middle, but it is on the top of the building closer to the last wraith (note this is the first lake bed with no scarab) and the wraith will most likely attack you while you try to get it.
No, it's until the AA Wraith is destroyed. IT IS THE AA WRAITH THAT SHOULD NOT BE DESTROYED. Destroy the normal one, but do not forget to keep the AA one alive.
