Find your first campaign skull.
Complete the level "Pillar of Autumn" on any difficulty.
Complete the level "The Silent Cartographer" on any difficulty.
Complete the level "Assault on the Control Room" on any difficulty.
Complete the level "Halo" on any difficulty.
Complete the level "Truth and Reconciliation" on any difficulty.
Complete the level "343 Guilty Spark" on any difficulty.
Complete the level "The Library" on any difficulty.
Complete the level "Two Betrayals" on any difficulty.
Complete the level "Keyes" on any difficulty.
Complete the level "The Maw" on any difficulty.
Complete any level with at least three skulls active on Heroic difficulty or higher.
Read a terminal.
Read half the terminals hidden throughout the campaign.
Read all of the terminals hidden throughout the campaign.
Locate half of the skulls hidden throughout the campaign.
Locate all the skulls hidden throughout the campaign.
Complete every level of the game on Normal difficulty.
Complete every level of the game on Heroic difficulty.
Complete every level of the game on Legendary difficulty.
Complete any level on Normal difficulty cooperatively.
Complete any level on Heroic difficulty cooperatively.
Complete any level on Legendary difficulty cooperatively.
Complete any level on Heroic difficulty or higher without taking health damage.
Complete the level "Pillar of Autumn" on Legendary without picking up an Overshield.
Complete the level "Pillar of Autumn" on Legendary without picking up a health kit.
Destroy three of the four Banshees on "Halo" on any difficulty during a single play-through.
Complete the level "Halo" on any difficulty without entering a vehicle.
Complete the level "Truth and Reconciliation" with at least four rounds left in your Sniper Rifle.
Pilot a Banshee on the level "Assault on the Control Room."
Kill 50 Flood Combat Forms on the level "343 Guilty Spark" on Heroic difficulty or higher.
Complete the level "The Library" on Heroic difficulty or higher without dying.
Complete the level "The Library" on Legendary difficulty in 30 minutes or less.
Complete the level "Two Betrayals" on Heroic difficulty or higher without killing any Grunts.
Complete the level "Two Betrayals" on Legendary difficulty without picking up a new weapon.
Kill 100 Flood Infection Forms on the level "Keyes" on Heroic difficulty or above.
Kill all the enemies in the first encounter of "Truth and Reconciliation" without being detected.
Storm the beach of "The Silent Cartographer" with no marine casualties on Heroic or Legendary.
Escape the map room in "The Silent Cartographer" without firing a shot on Heroic or Legendary.
Destroy four Wraith tanks in "Assault on the Control Room" with the Scorpion tank, in a single play.
Escape the Forerunner facility on the level "343 Guilty Spark" in 21 minutes or less.
Kill every Elite on the level "Keyes" on Heroic difficulty or above.
Complete the Warthog ride on the level "The Maw" without being forcibly ejected from your vehicle.
Escape "The Maw" on Legendary with at least a minute left on the count down.
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