In halo 3, I cant find the thunderstorm skull?

[evanm56]

I started at the beginning, on normal even tried on legendary, the ramp the skull is on is empty in the videos ive seen, but there are enemies up there in my game. No matter what I do it is never there. I dont think Im doing anything wrong. Does anyone know why this is happening?

 

[Matt s]

Youtube tutorials on the skull, number two you should turn on the skulls by being in a difficulty of at least noram and while on level selection press x and acivate the skulls to be on.