Halo 3 Skull location problem The IWHBYD?

[grenadestick]

Its not there each time i try it i even tryed it on heroic PLEASE HELP!!!

 

[iluvpandas]

heres some rules in completing that.
-I think it has to be on at least normal to unlock.
-when about to do it (at the part of the level) wait till you kill the prophet and clear out all the flood.
- DO not jump through the rings at any time before clearing out the flood.
- be sure to have the right sequence.