Some halo 3 skulls wont show up, please help!?

[sironicus]

Ok, one of the ones that wont show up is...the won called iron something at the end o sierra 117. the other one is thunderstorm...i go to all the right places but theres nothing.....and all skulls on the ark arnt thee ether...., anyone know why?

 

[xi3reakeroi3cx]

You need to be playing on Normal Mode or Higher.

Also, you have to start at the very beginning of the level and proceed through the entire level up to the point where you receive the skull in order for the skull to appear.

So if you're starting at a checkpoint hoping to find the skulls real quick and easy like, too bad. Start at the beginning.

 

[wylde95 A.R.T.]

If you are playing on easy mode they won't be there
You need to play on Heroic or higher.

(They might be there on Normal)