Skulls weren’t always a part of the Halo series, having only been introduced in Halo 2. These hidden objects serve to modify basic gameplay. Once activated, these skulls can make the game more challenging by altering it significantly.
In Halo 2 and in Halo 3, you had to first find these skulls within the games’ single player campaign to unlock them in order to use them. Like Halo Reach, you won’t have to do that this time around, as they’ll all be available for you to use at the start. It might be super disappointing to know that there are absolutely no new skulls available in Halo 4—not even ones like the Grunt Funeral skull from Halo: Combat Evolved Anniversary.
Indeed, they’re not even really “skulls”, but rather mods that you can flip on and off like in Reach and ODST. We can’t imagine that hiding these little skulls around in the single-player campaign would’ve been that hard to do, but we’ll take what we can get.
Fortunately for the achievement hunters among us, the 343 Industries was more than happy to scatter the single-player campaign with numerous Terminals to scratch that particular itch. That’s in addition to other secrets, of course, but we’ll have to come back to that later. If you’re keen on finding the Terminals, we’ve prepared a guide for that here.
Back to the skulls: it’s good to know that the Cloud skull from Halo: Reach (similar to the Fog skull in Halo 3) made it into the Halo 4, so if hunting blind is something you’re keen on, be sure to enable it.
Halo 4 Skull: Iron
Co-op - back to previous checkpoint on death. Solo - restart mission on death.
Halo 4 Skull: Black Eye
Shields don't recharge unless you melee enemies.
Halo 4 Skull: Tough Luck
Enemies always go beserk, always dive out of the way, never flee.
Halo 4 Skull: Catch
Enemies are grenade happy!
Halo 4 Skull: Cloud
Motion sensor is disabled.
Halo 4 Skull: Famine
Weapons drop much less ammo.
Halo 4 Skull: Thunderstorm
Major upgrade to the capabilities of enemies.
Halo 4 Skull: Tilt
Enemy resistances and weakness are increased.
Halo 4 Skull: Mythic
Enemies have increased health.
Halo 4 Skull: Blind
The HUD and the first person arms and weapons are hidden.