What level difficulty must you be on to get skulls in Halo 3?

[Bob S]

I got the game yesterday and beat it on easy, didn't find any skulls... Are some skulls found on specific difficulty levels?

 

[Harrison G]

anything harder than easy difficulty
and you can do it with a friend.

 

[Brice B]

Any difficulty but Easy

 

[peter h]

i believe any, but when my friend and i played the campain coop on heroic, they were there. try heroic, it isnt too hard, especially if you have a buddy.