i know its on top of the silo but i go up there and its not there and i didnt kill the purple wraith only the AA wraith
you need to pass the level in different kinds of level like legendary or heroic or normal.
you cant kill either wraiths. you hve to deal with them shooting you and gernade jump up there.
You have to be on normal, heroic, or legendary. Sometimes the skull is not tehre. I do not now why. Just restart the leverl
Ok the same thing happened to me but all i did was borrow my friends Halo 3 and its there. You either should complete the campaign on Normal and then check or go on to Xbox Live and play with somebody who already got it or like i said at first borrow your friends Halo 3( thats if its working on his)
