Halo 3 rocks!

adopt your own virtual pet!

Mark VI: Default Unlocked
CQB: Default Unlocked
EVA: Complete Campaign on Normal, Heroic, or Legendary
EOD: Complete Campaign on Legendary
Hayabusa: Collect all skulls
Security: Get all achievements in Halo 3.
Scout: Complete "Used Car Salesman" Achievement
ODST: Complete "Spartan Graduate"
Mark V: Complete "UNSC Spartan"
Rogue: Complete "Spartan Officer" Achievement
Recon: Bungie Employees and selected few.
Flaming Helmet: Bungie Employees only
Shoulder Pieces
Mark VI: Default Unlocked
CQB: Default Unlocked
EVA: Complete The Ark on Normal, Heroic, or Legendary
EOD: Complete The Ark on Legendary
Hayabusa: Collect 9 skulls[verification needed]
Security: Get 750 of 1000 game score on Halo 3[verification needed]
Scout: Complete "Mongoose Mowdown" Achievement
Recon: Bungie Employees and selected few
Chest Armor
Mark VI: Default Unlocked
CQB: Default Unlocked
EVA: Complete Tsavo Highway on Normal, Heroic, or Legendary
Hayabusa: Collect 5 skulls
Katana (Add-On)[2]: Earn 1000 out of 1000 Gamer score Points for Halo 3[3]
EOD: Complete Tsavo Highway on Legendary


Level: Tsavo Highway [1]
Directions: There is a point in this level where there is a shield that is blocking all vehicles from passing it. Disable the shield and fend off the drones that follow. Proceed through the tunnel and you will be on Tsavo Highway. To your left there should be a distinguishable yellow ladder. Safely jump down on the other side of the ladder facing away from you. The support beam creates a slight bridge that goes into the cliff. At the end of this bridge there is a cliff to your left. On the cliff you should find the Tough Luck skull.
Catch
Level: The Storm [1]
Directions: In the outdoor area with an AA Wraith, some Ghosts, and later a normal Wraith, there is a silo-like building past the boathouse near the edge of the cliff. Get up onto it using a vehicle and a grenade or an ally (Alternatively, you can park a Ghost next to the silo and then park a Warthog on top of it as a ramp, but this may take some practice, you can also park the 'Hog next to the lowest edge of the silo roof and deploy a bubble shield on top of the warthog as a ramp. Alternatively, if the Warthog is destroyed, it is possible to stand on a ghost and grenade jump to the roof), and the skull will be there. Note that if the non-AA Wraith's driver is killed (whether or not the Wraith is destroyed), the skull will disappear. This skull can be seen from other locations, including the boathouse where the battle rifle is located and the landing where the regular Wraith is located. If the skull disappears, go back to your last saved checkpoint.
Note: There is a glitch in some games where this skull will not appear, even if the other instructions have been followed. In such an event, you should complete the entire campaign on at least Normal difficulty. Also note that the skull itself is affected by physics, so if a Wraith’s plasma mortar hits the top of the silo, the skull may be lost. Further Note: This "glitch" that the note above refers to is if you kill any of the wraiths the skull will disappear.
[edit] Famine
Level: The Ark[1]
Directions: Method A At a point in the level, you will be directed into a fork in the road. Going straight will lead you into a giant bowl-like valley, and going to the right will lead you through a passage about 40 feet wide. Go to the right. When you get underneath the platform structure, you will notice some climbable rocks on the right that will lead you to the platform itself. You will notice several beam-like supports alongside the platform. Go the very last one, at the end of the platform. Align yourself close to the support. You need to get to the crevice of it, sticking out and away from the platform. Get about 6 feet away from the incline, and throw a plasma grenade to the top of the incline. It will stay there, because the incline rises about 3 inches before it goes downward. As you throw, begin a jump toward the crevice of the support. If you timed it right, you should be about 5 feet past the grenade when it explodes, which should give you the boost you need to get onto the support and get the skull. The timing might take a few tries before you get it right.
Directions: Method B A slightly easier way to get the skull is to use a Brute Chopper. Save one from an earlier battle, and then drive it to the part that's underneath some kind of roof (this is where you're going anyways) drive out from underneath it, and you should be making a right turn. To the right, on the rock face, there is a lone boulder on the ground. Drive slightly past it, then turn around, aiming at the bridge, and drive up the steep face. Eventually, you will be at a small gap between the bridge and the rock. on the left "edge" of the rock, you can see a small upwards incline. Using this as a jump, boost off of it and try to land on the bridge. This will probably take a few tries. Once you're on, turn left and drive to the last "pillar" (which contains the skull) hugging the pillar, drive the Chopper as close to the edge as possible. Then just jump on top of the Chopper, and jump into the pillar. Getting the Chopper just right and getting into the pillar takes a few tries, so don't be discouraged if you miss and take a while.
Directions: Method C When killing Brutes in the level pick up a deployable cover and drop it in front of the pillar with the skull and use it as a step to the ledge.
Directions: Method D It's almost certainly possible to use a Rocket Launcher, Brute Shot or even a non-explosive weapon to shoot the skull off its perch and simply pick it up when it falls to the ground. However, upon testing this theory with grenades, battle rifles, the covenant sniper equivilant, a plasma rifle, and an assault rifle, I found that no matter how I aimed, whether or not i was hitting the skull, Mr. Skully refused to budge. Piling two ghosts on top of each other with another player crouching below me led to success.
[Edit] Tilt
Level: Cortana [1]
Directions: The skull is at the top of the large circular room where Cortana asks your name, and says it’s very nice to meet you and that she likes to play games too.(your screen and movement won’t change for this one). To the left of the room will be some small, somewhat fungal, growths on the walls. Using these, jump up onto a platform. There will be some more nearby, so use those to get to a large circular platform with the skull on it. The skull will not be there after you reach the next save point.
Icon: A skull marked with a smaller skull with a hole in its head.
Effect: Enemy resistances are greatly increased. Where a particular type of weapon normally does slightly increased damage (ex. projectiles against Brute flesh, or plasma against Brute armor), it is instead greatly reduced.
Point Multiplier: 2x


Scout: Complete "Too Close to the Sun" Achievement

If you get all 13 skulls you get the Hayabusa armor
So if you need any help, just post!

In Halo 3 you can get 13 different skulls. only 12 of the make the game harder, the other one is just a comic effect. if you kill a short alien with a head shot confetti comes out and you hear little kids screaming. If you need any help just post on my blog.