Halo: Combat Evolved Anniversary

This skull which gives you unlimited ammo can be found on the fourth mission: The Silent Cartographer, after the covenant lock the doors you have to go to the security override building. In the tunnel before activating the console, turn right, go outside then turn right again and you should see the exterior of the tunnel you came through, the skull is on top of this tunnel at the far end. To get to it, you need to grenade jump (throw a grenade, jump and the force of it makes you jump higher) onto the structure and grab the skull.

This skull which when turned on, only melee attacks restore your shields can be found in "The Library" and requires a grenade jump (Throwing a grenade at your feet and the force of it should propel you higher) , It is located right at the start before you enter the big round room where the index is located. There are vents on the wall where flood come out of. With your back facing the entrance to the index chamber, the skull is located in the vent to your right, grenade jump on to the platform in front of it then jump normally into the vent, move towards the end of the vent and you should pick it up.

"Explosions have twice the damage radius. Light fuse, run away." This skull can be found in "Halo" right before the tunnel. When approaching the tunnel by warthog, drive to the right, get out, and walk up the narrow path until you reach the skull.

In "Assault on the Control Room," you can get a banshee shortly after the tank. Take the sniper rifle and the rocket launcher. Clear the enemies, and then go to the boulder on the right side of the tunnel. Look up and you will see a rock bridge. Now, while still looking up, start moving forward until you see a platform coming out of the wall. Zoom in with the sniper rifle to the center of the platform, and then without moving change to the launcher and fire. A banshee will fall off the ledge, and you can use it.

Equip the pistol and go behind a Hunter enemy. You'll see an orange spot on their back; hit the orange spot once and the hunter will die.