Skulls

All skulls do really is make the game more interesting like if you click on X befor you start a level you can change the game options and you can activate any skull you have grabed in story mode. I can't tell you the most favorited skull. It is in the level crows nest and it is under the walkway when you dropdown the hole and that blue figure pops up on your screenwhen you are about to drop down the giant vent to get to the aberter when he kills the 3 bug things look down there is a mini ledge right below the walkway you are on if you fall on it head backwords and the skull is right there but if you fall down the shaft use a grav lift to get up I have done it both ways so it works

Gold skulls:

Iron - If you die while playing alone, you will restart at the beginning of the level (you cannot revert to the last checkpoint at any time). If any player dies while playing co-operative, you will reset to the last checkpoint. This is similar to what would happen when playing co-operative on Legendary in Halo 2, but is slightly more harsh on the players.

Black Eye- Your Energy Shield will not recharge until you perform a melee hit. The Energy Sword and Gravity Hammer's R-Trigger attacks count as a melee attack. Hijacking also counts as a melee attack.

Tough Luck - Enemies dodge grenades, needles, and vehicle assaults with a far greater success rate. However, plasma and spike grenade sticks are still possible at close range, and from behind. Catch - All AI-controlled units, friend or foe, throw grenades more often, where applicable.

Fog - Your motion sensor is no longer active.

Famine - All weapons that are dropped by enemies or are scripted to spawn on the ground (e.g., near a downed Pelican or group of dead bodies) have halved or reduced ammunition or charge. However, weapons found in cases still have the regular amount of ammo.

Thunderstorm - All enemies (and Sangheili allies) are promoted to the highest available rank. The number of shielded Flood elite combat forms is also increased. Tilt - All enemy weaknesses and resistances double. Example: Brute armor is weaker to plasma weapons and stronger against projectile weapons. Mythic - All of the Covenant you encounter have twice the amount of health.

Silver skulls:

Blind - You lose all your HUD when this skull is turned on. You won�t see your weapons, shield, radar, etc.

Grunt Birthday Party - Arguably the most popular Skull, if a Grunt is shot in the head with any headshot-capable weapon (such as the Battle Rifle, Beam Rifle, Carbine and Sniper Rifle) confetti explodes out of it (the explosion causes minor damage to nearby enemies), and a sound clip of children cheering from the game Viva Pi�ata can be heard in the background

Cowbell - The force of explosions is increased immensely.

I Would Have Been Your Daddy (IWHBYD) - Unlocks new, often humorous, dialogs for the AI. Such as "THIS IS SPARTA!" or "Who wants ice cream!?" for some marines or "Pie is good" said by some Brutes. Sometimes a Brute may even say "He was my lover!" when you kill a nearby Covenant soldier, and Grunts may say "Stay close to me, Nipple-mate!" to another Grunt when they are suspicious that enemies may be nearby, or "Thank you for choosing Air Blue-Ball" as they go Kamikaze, Elites sometimes make humorous remarks when you exchange weapons or stare at them for long periods of time. Remarks like "I shall name my next child after you" or "I, I, I think you're sexy too."

All skulls do really is make the game more interesting like if you click on X befor you start a level you can change the game options and you can activate any skull you have grabed in story mode. I can't tell you the most favorited skull. It is in the level crows nest and it is under the walkway when you dropdown the hole and that blue figure pops up on your screenwhen you are about to drop down the giant vent to get to the aberter when he kills the 3 bug things look down there is a mini ledge right below the walkway you are on if you fall on it head backwords and the skull is right there but if you fall down the shaft use a grav lift to get up.