Note: Skulls only appear while playing on a difficulty other than easy and when you start from the beginning of a mission, not from a checkpoint.

One "side mission", of sorts, in Halo 3 are the skulls. Nine (9) gold skulls and four (4) silver skulls can be found in the game. There are a few reasons to locate the skulls within the game. The first reason is the challenge. They are fun to find, even if you know where they are, they can be a challenge to reach. Secondly, each GOLD skull gives you an achievement worth 10 points. The final reason, and the best reason, is that once you have a skull you can activate it in campaign mode. When activated, each skull adds a multiplying factor to the campaign scoring as well as an effect to the game play. What exactly do I mean by effect? The table below shows each skull’s multiplier value and effect. The first nine are gold skulls, the final four are silver skulls.

Halo 3 Skull Effects and Multipliers

Skull	Multiplier	Effect
Iron	3	If playing co-op and any player dies, everyone restarts from the last checkpoint. In single player, if you die you restart at the beginning of the mission.
Black Eye	1.5	Shields only recharge by hitting an enemy with a melee attack.
Tough Luck	1.5	Enemies avoid projectiles, vehicles, gernades, etc with greater success.
Catch	1.5	Enemies throw gernades... FAST.
Fog	1.5	No motion tracker for you.
Famine	2	Dropped enemy weapons have less ammunition.
Thunderstorm	1.5	All enemy units are upgraded one level.
Tilt	2	Enemy resistance increased. Armors that was highly resistive to human weapons gets 100% resistance.
Mythic	2	All enemies have double health.
Blind	N/A	Your heads-up-display (HUD) is turned off.
Grunt Birthday Party	N/A	Kill a grunt with a headshot and it explodes into confetti and the kids cheer!
Cowbell	N/A	BOOOM! Larger explosions in the game.
IWHBYD	N/A	Unlocks hidden dialogue in campaign mode.

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