Complete each achievement to get the allotted gamerscore.

Askar (10): Score over 15,000 points in the Campaign meta-game on the fourth mission
Assault (30): Finish the fourth mission of the Campaign on Normal, Heroic, or Legendary
Black Eye (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Campaign Complete: Heroic (125): Finish the Campaign on Heroic (normal is unlocked as well)
Campaign Complete: Legendary (125): Finish the Campaign on Legendary (normal and heroic are unlocked as well)
Campaign Complete: Normal (125): Finish the Campaign on Normal
Catch (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Cavalier (10): Score over 15,000 points in the Campaign meta-game on the third mission
Cleansing (30): Finish the fifth mission of the Campaign on Normal, Heroic, or Legendary
Demon (10): Score over 15,000 points in the Campaign meta-game on the second mission
Exterminator (10): Score over 15,000 points in the Campaign meta-game on the fifth mission
Famine (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Fear the Pink Mist (5): Kill 5 enemies with the needler in a ranked free for all playlist or in campaign
Fog (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Graduate (10): Earn 5 EXP or finish 10 games to complete the requirements for basic training (Online)
Guerilla (10): Score over 15,000 points in the Campaign meta-game on the first mission
Headshot Honcho (5): Kill 10 enemies with headshots in a ranked free for all playlist or in campaign
Holdout (20): Finish the second mission of the Campaign on Normal, Heroic, or Legendary
Iron (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Killing Frenzy (5): Kill 10 enemies without dying in any ranked free for all playlist (Online)
Landfall (20): Finish the first mission of the Campaign on Normal, Heroic, or Legendary
Last Stand (40): Finish the seventh mission of the Campaign on Normal, Heroic, or Legendary
Lee R Wilson Memorial (5): Score 5 grenade sticks in any ranked free for all playlist (Online)
Marathon Man (40): Locate and access all Terminals in the Campaign
Maybe Next Time Buddy (5): Board the same vehicle within 10 seconds after being boarded in any free for all playlist (Online)
Mongoose Mowdown (5): Splatter an enemy with the mongoose in a ranked free for all playlist (Online)
MVP (5): Earn the MVP in any ranked playlist (Online)
Mythic (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Orpheus (10): Score over 15,000 points in the Campaign meta-game on the eigth mission
Overkill (5): Kill 4 enemies within 4 seconds of one another in a ranked free for all playlist (Online)
Ranger (10): Score over 50,000 points in the Campaign meta-game on the sixth mission
Reclaimer (10): Score over 15,000 points in the Campaign meta-game on the final mission
Refuge (30): Finish the sixth mission of the Campaign on Normal, Heroic, or Legendary
Return (50): Finish the final mission of the Campaign on Normal, Heroic, or Legendary
Spartan Officer (25): Advance to the Spartan Officer ranks (Online)
Steppin' Razor (5): Score a Triple Kill with the sword in a ranked free for all playlist (Online)
The Key (40): Finish the eigth mission of the Campaign on Normal, Heroic, or Legendary
The Road (20): Finish the third mission of the Campaign on Normal, Heroic, or Legendary
Thunderstorm (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Tilt (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Too Close to the Sun (5): Destroy an enemy banshee with the spartan laser or missile pod in a ranked playlist or in campaign
Tough Luck (10): Find and claim this skull when playing on Normal, Heroic or Legendary difficulty
Triple Kill (5): Kill 3 enemies within 4 seconds of one another in a ranked free for all playlist (Online)
Two for One (5): Score a Double Kill with a single spartan laser shot in a ranked free for all playlist (Online)
UNSC Spartan (15): Earn your Sergeant rating to be recognized as a true Spartan (Online)
Up Close and Personal (5): Kill 5 enemies by melee or assassination in a ranked free for all playlist (Online)
Used Car Salesman (5): Destroy a vehicle that has three enemies in it in a ranked playlist or in campaign
Vanguard (10): Score over 50,000 points in the Campaign meta-game on the seventh mission
We're in for Some Chop (5)Destroy an enemy vehicle with equipment in a ranked playlist or in campaign