Yes, there are 13 skulls in Halo 3. Once the level is completed after they are found, here are their effects. Iron: If a teammate dies, you restart from last checkpoint. If everyone dies at once, you restart the entire level. Black Eye: Melee attacks cause shield regeneration. Shields no longer auto-regenerate. Tough Luck: Enemies can dodge most projectiles. They also go Berserk and go Kamikaze more often. Catch: NPCs throw more grenades, but leave two free grenades when they die. Fog: The motion tracker is disabled. Famine: Dropped weapons have half the initial ammo/charge.