Full list of all 73 Halo 5: Guardians achievements worth 1,250 gamerscore. It takes around 40-50 hours to unlock all of the achievements in the base game.
The base game contains 65 achievements worth 1,000 Gamerscore, and there are 2 DLC packs containing 8 achievements worth 250 Gamerscore.
Found and claimed all Intel.
Found and claimed all Skulls.
Used a Ground Pound on an exterior power core in Guardians on Heroic difficulty.
Knocked two Hunters into the ocean during the Battle of Sunaion.
Completed any Mission with 3+ Skulls active on Heroic difficulty.
Completed every Mission of the game on Heroic difficulty.
Completed every Mission of the game on Legendary difficulty.
Completed every Mission of the game by yourself on Legendary difficulty.
Finished the 13th mission without losing the Scorpion on Legendary difficulty.
Spectated a game.
Killed a Grunt and smashed a grate with a Ground Pound in Battle of Sunaion.
Escaped the doomed Kraken by jumping onto a Phaeton piloted by a Spartan.
Traversed the canyon without a Phaeton in Reunion on Heroic difficulty.
Destroyed 10 walls or floors in Swords of Sanghelios.
Completed Glassed without entering a vehicle.
Completed Glassed without any players using Smart-Link.
Completed any co-op Mission on Heroic difficulty.
Found and claimed a Skull.
Escaped the Hunters in the lab and fought them in the hangar in Blue Team.
Completed 5 matchmade games of Capture the Flag.
Completed 5 matchmade games of Strongholds.
Completed 5 matchmade games of Breakout.
Qualified for a Competitive Skill Rating.
Completed 5 matchmade games of Slayer.
Won a match on all three original Warzone maps.
Completed 3 matchmade games of Warzone.
Called in a REQ that costs 5 Energy or more.
Opened a Gold REQ Pack.
Killed a Legendary Boss in Warzone.
Completed every Mission of the game on Normal difficulty.
Completed Mission 15.
Completed Mission 14.
Completed Mission 13.
Completed Mission 12.
Completed Mission 11.
Completed Mission 10.
Completed Mission 9.
Completed Mission 8.
Completed Mission 7.
Completed Mission 6.
Completed Mission 5.
Killed an enemy that's had its armor repaired in Unconfirmed.
Completed Mission 4.
Completed Mission 3.
Completed Mission 2.
Completed Mission 1.
Found and claimed one piece of Intel.
Commanded your team of Spartans in Osiris.
Changed your Emblem in the Spartan Hub.
Changed your Service Tag in the Spartan Hub.
Changed your Spartan's gear in the Spartan Hub.
Create and save a Custom Game.
Finish Evacuation within 18:00 without dying on Heroic difficulty.
Help the Elite General charge the hill in Osiris on Heroic difficulty.
Simultaneously assassinate two Elites in Blue Team co-op.
Team up in a vehicle to kill 30 enemies in Unconfirmed co-op.
Keep 6 miners alive at the elevator in Evacuation on Heroic difficulty.
Destroy the Phantom at the Covenant camp in Reunion on Heroic difficulty.
Complete Swords of Sanghelios co-op with both Mantises on Heroic difficulty.
Complete Enemy Lines without destroying a Kraken turret.
Operate four different vehicles at once in Mission 13 on Heroic difficulty.
Complete The Breaking on Legendary difficulty without the entire fireteam dying.
Simultaneously kill two Wardens in The Breaking on Heroic difficulty.
Simultaneously destroy 2 cores in Guardians on Heroic difficulty.
Complete every co-op Mission on Heroic difficulty.
Beat the par time of a mission in Score Attack.
Completed a mission in Score Attack with at least 10,000 points.
Reached 50,000 points in Score Attack with a Skull multiplier of x2 or higher.
Completed a mission in Score Attack with at least 500,000 points.
Complete a mission in Score Attack co-op, with all participants scoring at least 200,000 points.
Successfully completed 5 Warzone Firefight matches.
Completed a Warzone Firefight match on 6 unique maps.
Earned a Mythic Boss Takedown in a Warzone Firefight match.