No missable achievements (plus 73 unknown)
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Commanded your team of Spartans in Osiris.
Completed Mission 1.
Found and claimed one piece of Intel.
Completed Mission 2.
Changed your Emblem in the Spartan Hub.
Completed Mission 3.
Completed Mission 4.
Completed Mission 5.
Completed Mission 6.
Completed Mission 7.
Changed your Spartan's gear in the Spartan Hub.
Killed an enemy that's had its armor repaired in Unconfirmed.
Completed Mission 8.
Completed Mission 9.
Completed Mission 10.
Completed Mission 11.
Completed Mission 12.
Changed your Service Tag in the Spartan Hub.
Completed Mission 13.
Opened a Gold REQ Pack.
Completed Mission 14.
Completed Mission 15.
Completed 5 matchmade games of Slayer.
Called in a REQ that costs 5 Energy or more.
Completed 3 matchmade games of Warzone.
Completed every Mission of the game on Normal difficulty.
Killed a Legendary Boss in Warzone.
Qualified for a Competitive Skill Rating.
Earned a Mythic Boss Takedown in a Warzone Firefight match.
Completed 5 matchmade games of Breakout.
Found and claimed a Skull.
Completed 5 matchmade games of Capture the Flag.
Won a match on all three original Warzone maps.
Completed 5 matchmade games of Strongholds.
Successfully completed 5 Warzone Firefight matches.
Completed any co-op Mission on Heroic difficulty.
Completed a Warzone Firefight match on 6 unique maps.
Completed Enemy Lines without destroying a Kraken turret.
Spectated a game.
Completed every Mission of the game on Heroic difficulty.
Created and saved a Custom Game.
Completed a mission in Score Attack with at least 10,000 points.
Completed every Mission of the game on Legendary difficulty.
Escaped the Hunters in the lab and fought them in the hangar in Blue Team.
Completed every Mission of the game by yourself on Legendary difficulty.
Completed every co-op Mission on Heroic difficulty.
Finished the 13th mission without losing the Scorpion on Legendary difficulty.
Traversed the canyon without a Phaeton in Reunion on Heroic difficulty.
Completed Glassed without any players using Smart-Link.
Beat the par time of a mission in Score Attack.
Completed any Mission with 3+ Skulls active on Heroic difficulty.
Completed Glassed without entering a vehicle.
Found and claimed all Skulls.
Destroyed 10 walls or floors in Swords of Sanghelios.
Found and claimed all Intel.
Used a Ground Pound on an exterior power core in Guardians on Heroic difficulty.
Escaped the doomed Kraken by jumping onto a Phaeton piloted by a Spartan.
Finished Evacuation within 18:00 without dying on Heroic difficulty.
Operated four different vehicles at once in Mission 13 on Heroic difficulty.
Killed a Grunt and smashed a grate with a Ground Pound in Battle of Sunaion.
Kept 6 miners alive at the elevator in Evacuation on Heroic difficulty.
Teamed up in a vehicle to kill 30 enemies in Unconfirmed co-op.
Simultaneously assassinated two Elites in Blue Team co-op.
Reached 50,000 points in Score Attack with a Skull multiplier of x2 or higher.
Completed Swords of Sanghelios co-op with both Mantises on Heroic difficulty.
Completed a mission in Score Attack with at least 500,000 points.
Simultaneously destroyed 2 cores in Guardians on Heroic difficulty.
Destroyed the Phantom at the Covenant camp in Reunion on Heroic difficulty.
Helped the Elite General charge the hill in Osiris on Heroic difficulty.
Completed a mission in Score Attack co-op, with all participants scoring at least 200,000 points.
Knocked two Hunters into the ocean during the Battle of Sunaion.
Completed The Breaking on Legendary difficulty without the entire fireteam dying.
Simultaneously killed two Wardens in The Breaking on Heroic difficulty.