Halo 2 skulls

Summary
A Skull in Halo 2 is an easter egg left in by Bungie to make the game more challenging or interesting, or to unlock potentials that would otherwise remain hidden. There is no information text to wield a skull, as there is with a weapon, but it can be picked up just the same, and it's effect, ranging from making the game extremely difficult to letting one grenade jump higher than ever before, lasts until the XBox is restarted, but do nothing in non-campaign split-screen. These skulls are hidden very far out of the normal path of the level, sometimes even backwards.

Every skull except the Blind Skull, Assassin Skull, and the Envy Skull, although Assassin and Envy have no effect on other difficulties, are only available in Legendary Difficulty. The Blind skull is a very handy tool when recording video, and therefore is very easy to activate.

Note: These items are not actually part of the Halo universe, but are just tidbits Bungie left in Halo 2.

Also, they are technically not skulls, as they all are missing the lower jaw. They are actually craniums

Skulls video
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Anger
Level: Gravemind

Directions:  When you are the Master Chief trying to recover the index from the Prophet of Truth on the Covenant Holy City go until you reach the first outdoor area with dirt and vegetation. Take a right as you enter this room and run up to the wall past the gravity lift that leads up to the sniper point. Get on top of the wall by going up the dirt mound on your left. Follow the wall until you reach the floating skull called "Angry". Effects: Enemies fire their weapons faster and alot more.

Difficulty: Legendary

Assassins
Level: Regret

Directions: Immediately after the gondola ride following the battle with the Hunters, there will be a building with two turrets on it. Enter the building and turn to your right. There will be a box, jump on it. From there jump to the adjacent light fixture, then to the ledge. The ledge leads to the area with the two turrets. Once there use a Grenade Jump to get onto the roof area, then, using Crouch Jumps and grenade jumps, follow the right side perimeter of the building. Once you have gone as far as you can go you will find a small grassy area with two cloaked Elites (that cannot be assassinated) in their "angry stance" and the Assassins skull.

Difficulty: Legendary

Effect: All enemies in game are permanently cloaked. Marines can't see them, so they can't help at all!

Status: Confirmed

Also: This skull also appears on any difficulty but will not affect unless is on Legendary.

Black Eye
Level: The Great Journey

Directions: Eventually you have to escort the Sarge who is in a Scarab. Follow him along until you see the huge compound in front of you. Directly above the door that the Sarge blows open with the Scarab is an angled beam. Land your Banshee on this beam and walk to the top of the beam. Look down and to your left and you will see a circular angled wall. Jump onto this wall and walk to the top. Walk straight along the right-hand side of this area. You will have to jump over a small beam in front of you. Continue walking straight until you come to a grassy area. Keep walking up the grassy hill and go until you come to the point where can jump onto the angled support for the tower meets the grass. Jump onto the support and walk up the support. It's a very steep climb, so jumping while you're going up the support speeds up the walk some. At the first landing you will see the Black Eye skull sitting on a glowing white panel on the floor.

Difficulty: Legendary

Effect: Your shield does not charge normally. To charge your shields you must kill something (enemy or ally) with a melee attack (anything but the Energy Sword). You can charge your shields into the Overshield range by doing this. Also activates subtitles during cut scenes.

Status: Confirmed

Blind
Level: Outskirts

Directions: At the beginning of Outskirts, run to the door and go in, there will be a Grunt down the hall. If you go through the door there will be another door painted onto the scenery. Jump onto the light above the door and crouch-jump onto the wall. Turn to your left and go down the long dark corridor and pick up the skull beside the grenades; it will say "blind" and your screen will flash black for a second.

Difficulty: Any difficulty

Effect: Your HUD becomes invisible. In other words, you cannot see your weapon (unless it's the Energy Sword), body, shields, ammo, or motion tracker, or use your flashlight. Good luck aiming with no reticle! Also, enemies can still spot you, ergo, this skull serves no tactical advantage whatsoever, although hitting enemies with the skull should kill them with only two or three hits. After you die the effect of Blind will keep happening until you quit the game.

Status: Confirmed

Catch
Level: Metropolis

Directions: Right after you exit from the underground highway, you'll come to a large open-air circular room with a handful of Jackal snipers and some Elites. The quickest way to get safely to the skull is to get the next checkpoint by jumping into the Warthog and letting the Marine drive you to the next area. Jump out of the jeep and backtrack to the large room, and clear the area. Or you can get your warthog from the bridge and just run right through the platforms and the other part until you reach the place where you find the wraiths attacking the building where the marines are (but you don't have to fight them) and then go back and the enemies will be gone when you go back. You will see a large semi-circular beam going from one of the main platforms that goes from the ground up to the top of the two towers. Do a grenade jump at the bottom of this beam and walk all the way to the top. Jump over to the ledge of the left tower. Walk to the end of the ledge and you will find the Catch skull.

Difficulty: Legendary

Effect: AI will toss more grenades. Also, everybody (allies and enemies) will drop two grenades.

Status: Confirmed

Envy
Level: Delta Halo

Directions: Progress through Delta Halo until you come to an area with a large central structure that has a multitude of columns. This is the area where Cortana tells you that the Covenant is pouring out of the center section. When you first get into this area, you have to go left, and there is a ramp on the left that goes up and then back down. Get on this ramp and continue up the wall until you are on the landing where there will be (or used to be) some plasma turrets. Follow this landing all the way to it's end, and you'll see a door that is blocked off by a large stone. Jump on top of the stone, and jump again to get on a thin ledge. Make sure you're up against the left wall, and grenade jump up to the top of the wall to your left. Once you're on this wall, you'll see that the right wall ends and there is some earth behind it. Jump onto the dirt, and follow the stone wall all the way to the top. When you're on the top of this wall, you can look down towards the center and you should see two cloaked Elites repeating their "angry stance" towards each other with the Envy skull between them.

Difficulty: Legendary

Effect: The Master Chief now has an active camouflage device just like the Arbiter's. However, there is no visible timer, so remember: 5 second cloak with 10 second recharge. To fully exploit the effects of this skull, execute the Permanent invisibility glitch.

Status: Confirmed

Famine
Level: The Oracle

Directions: After you get off of the slowly descending elevator, you will come to a hallway where you see a handful of dead bodies. Continue into the next room, and you will be on the second floor of a room that has a lot of glass windows. When you enter this room, look to the right, and find the third pane of glass. It should be to the right of a wall that has some flood guts splattered on it. Shoot out this window, and the windows directly across the room. If you look below you, you will see a platform that has four tall posts. On the far side of the room there is a column that is right in between the two windows on the far side of the room. Turn on your active camo, and jump to the center platform. Jump on either of the posts on the far side of the platform and jump to the column between the windows. Make another jump through the window you shot out, and make a left. Walk all the way to the end and you'll find four Combat Form Elites convulsing on the floor, with the Famine skull in the middle of them. Sometimes, one of the combat forms stands up, but it does not attack.

Difficulty: Legendary

Effect: All weapons found on the ground have half ammo. Plasma weapons and lasers remain unaffected.

Status: Confirmed

Ghost
Level: Uprising

Directions: Immediately after the armory room that is full of Covenant and human weapons, there is an L shaped room. Grenade jump using a Ghost up to the rafters of this room, and you will find the skull over a doorway. Or, if you are playing co-op, get a box from the weapon room, and have one player stand on the box, then have the other player stand on the first player's head, have player 2 crouch-jump on to the ledge and grab the skull!

Difficulty: Legendary

Effect: When meleeing an elite or other enemy, they do not flinch. It is also said that enemies take a longer time to notice your presence.

Status: Confirmed

Grunt Birthday Party
Level: The Arbiter

Directions: The very first time you get a Banshee, fly down. Below you is a large beam-like structure (not to be confused with the one directly below you that turns and goes vertical) running from the arm of the station you just came out of to one exactly like it on the side opposite. Below this structure are 3 cylinders hanging down, with cylinders of light shooting out of the bottom. They look like they are what keeps the station floating. If this explanation is too vague, they are the absolute lowest parts of the station. Now go to the middle engine and land on the top part of it. This and the other engines connect to the large structure mentioned earlier. The tops of the engines come up to meet the structure at an angle, where this angle is under the connecting structure and coming up to meet it, there is a place to walk (like being under a bridge). Under one side you will see the six Heretic Grunts dancing in a circle around the Skull.

Difficulty: Legendary

Effect: Headshots turn into Plasma Grenade explosions. You must first take down an Elite's shield for this to work on one. You can also give a headshot to a dead body and it will still explode. This skull doesn't have effect against Hunters nor Drones. Note: you can combine this with the Sputnik skull, this will make the explosions really powerful and amusing. (it is also A LOT easier to obtain with the Sputnik skull)

Status: Confirmed

I Would Have Been Your Daddy
Level: Outskirts

Difficulty: Legendary

Directions:This is by far the hardest skull to obtain. Mainly because it only appears once every seven times. You must jump onto the roofs and work your way to the area next to snipers alley without going through it. Getting seven checkpoints in the process helps as well as killing at least seven enemies. Dying before getting the skull has no effect on the chances of it spawning. There are multiple videos that can be found, detailing the path to find it. Picking it up will transport you to Sniper Ally armed only with a plasma pistol, and faced with seven waves of Ultra Elites. There's one in the first wave, two in the second, etc. You have to kill all the Elites for the skull to take effect. If you die, the skull will have vanished and you will have to start at the beginning, unless you reach a checkpoint after finding the skull. This can be avoided altogether if you simply Revert to last checkpoint instead of waiting to respawn. It helps immensely if you get the Envy or Ghost skull first. The battle against the elites is aggravating. Getting the Infinite Camo trick will help a lot also. NOTE: It will probably take nearly two hours to get this skull.

Effect: The rarity of combat dialog is changed, rare lines become far more common but common lines are still present at their normal rate..

Status: Confirmed

Trivia: The skull is named after a Sergeant Johnson quote sometimes heard in Assault on the Control Room: "I would have been your daddy, but the dog beat me over the fence!" Sergeant Stacker also occasionally says this on the Silent Cartographer. The first chapter of Assault on the Control Room is also named "I Would Have Been Your Daddy."

Iron
Level: High Charity

Directions: When you enter the final (the second) Gravity Lift, look up. A skull will pass through you extremely quickly so you must start holding X a bit before you actually pass it to grab hold of it.

Difficulty: Legendary

Effect: When playing co-op, if either player dies the game restarts you at your last checkpoint. Also, on other sites it may state that allies are immune to melee attacks - that is false.

Status: Confirmed

Mythic
Level: Sacred Icon

Directions: There is a semi outdoor area which has the same type of area right next to it. There is an Enforcer in front of each one. Go past this area and down the piston and you'll be in a vary dark and dank Flood infested area. There's a stack of 6 or 7 boxes as you enter the room. Use them to jump up to the landing above. There are a handful of alcoves on your right hand side. The skull is in the third alcove, floating above a dead human Flood.

Difficulty: Legendary

Effect: Turns on 'Mythic' difficulty (which makes sense, as it comes after Heroic and Legendary). Enemies have more health and shielding, and are therefore harder to kill. Note: health and shielding increase more as the enemies rise in rank. A red Grunt will not gain as much health as a white Grunt. Similarly, a blue minor Elite will gain a small bit of health, but a white SpecOps Elite will gain a ridiculous amount of both shielding and health, to the point that a Plasma Overcharge won't drop their shields even halfway. Besides that, it also makes your allies gain a small bit of health.

Status: Confirmed

Sputnik
Level: Quarantine Zone

Directions: From the start of the level, turn directly around, and you should see a tunnel. Head into the tunnel and go straight until you exit the tunnel. Go straight across the open area, and you'll come across a broken pipe tunnel on your right. Straight in front of you you should see a small ledge running across the wall, above the green pit. Carefully get onto that small ledge and walk all the way to the end of the ledge to find the Sputnik skull.

Difficulty: Legendary

Effect: The mass of certain objects is severely reduced, making them fly farther when smacked with a melee hit, or when they are near an explosion. Weapon damage seems to have strengthened slightly. It also has the added effect of making enemies turn around when you hit them, allowing you to kill them in two hits. With the Sputnik Skull's effect in place, players can reach nearly impossible to get to places and much higher altitudes using grenade jumps. Also you can move dead bodies.

Status: Confirmed

Thunderstorm
Level: Cairo Station

Directions: In the large room after the armory, you need to use a crouch-jump to get onto a light fixture on the right wall (right of the room when you enter) and then jump from there onto the higher area. There is a series of diagonal beams. Walk up one near to the end of it and use it to duck-jump onto one of the rails. You can fall between the rails, so be careful. Once on the rail, walk down it until you can jump onto the highest platform. Then bash the trashcan.

Difficulty: Legendary

Effect: All Elites (Except "fixed" variants, e.i. Jet-pack, Spec-Ops), Grunts (Also except fixed variants, like gunner etc.), Jackals (Except snipers), and Brutes become their highest rank. All Covenant Flood forms have shields. All Sentinals are of the gold variety and have shields.

Note: Elites will not become Gold Commanders, but Ultra Elites.

Bonus:Thunderstorm on Normal 

This glitch is really easy to perform. Just start Cairo Station on Legendary, get to the Skull, then save, quit, and switch to another profile. Now, start Cairo Station on Normal. All the Elites and Grunts are Ultras (Sweet!). This makes gameplay a little harder because they shoot faster, the Grunts throw accurate grenades, and all the Elites have Swords as a secondary weapon, but its still awesome- and it only works once. To try it again, you have to go through the whole process all over again.

Status: Confirmed

Unnamed Skull
Level: The Armory

Directions: At the beginning of the level, after you power your shields for the first time, the Sarge shows up on an elevator. Wait in the room until the Sarge starts berating you, telling you to get into the elevator. You MUST wait for him to say "Would it help if I said please?" Once he says this, get in the elevator, and go down to the tram. Get on the tram, and face towards the INSIDE of the building. Press up against the glass doors towards the inside of the building. You should hold X down, and you should pick up the skull. It's on a stack of green crates, near the end of the tram ride.

Difficulty: Legendary

Effect: Stregnthens the Artificial Intelligence of both allies and enemies. Enemies will notice the slight shimmer of active camoflauge, your characters shadow, the sound of you reloading, along with many other subtle clues which help them find you. All computer controlled characters have better accuracy, and will no longer blow themselvs up with a Rocket Launcher. A common misconception is that it makes enemies more aware of your location, however it does not. Status: Confirmed.

Trivia

 * The file in the H2 code nicknames the Unnamed skull 'whuppopotamus', although no name for the skull appears in-game. It has been called the "Monkey Skull", though. But still nothing official.
 * The skulls were actually created to make the game harder and/or more fun varying

Campaign Order

 * 1) The Heretic: N/A
 * 2) The Armory: Unnamed Skull(You no hide from me)
 * 3) Cairo Station: Thunderstorm
 * 4) Outskirts: Blind & I Would Have Been Your Daddy
 * 5) Metropolis: Catch
 * 6) The Arbiter: Grunt Birthday Party
 * 7) The Oracle: Famine
 * 8) Delta Halo: Envy
 * 9) Regret: Assassins
 * 10) Sacred Icon: Mythic
 * 11) Quarantine Zone: Sputnik
 * 12) Gravemind: Anger
 * 13) Uprising: Ghost
 * 14) High Charity: Iron
 * 15) The Great Journey: Black Eye