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.
Killed a Grunt and smashed a grate with a Ground Pound in Battle of Sunaion.
Helped the Elite General charge the hill in Osiris on Heroic difficulty.
Completed any Mission with 3+ Skulls active on Heroic difficulty.
Spectated a game.
Completed every Mission of the game on Normal 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.
Completed Mission 15.
Completed Mission 14.
Completed Mission 13.
Finished the 13th mission without losing the Scorpion on Legendary difficulty.
Killed a Legendary Boss in Warzone.
Completed Mission 12.
Completed 5 matchmade games of Breakout.
Won a match on all three original Warzone maps.
Completed Mission 11.
Completed Mission 10.
Completed Mission 9.
Completed Mission 8.
Destroyed 10 walls or floors in Swords of Sanghelios.
Completed Mission 7.
Traversed the canyon without a Phaeton in Reunion on Heroic difficulty.
Completed Mission 6.
Completed Mission 5.
Completed Glassed without entering a vehicle.
Completed Glassed without any players using Smart-Link.
Completed 5 matchmade games of Capture the Flag.
Killed an enemy that's had its armor repaired in Unconfirmed.
Completed Mission 4.
Completed Mission 3.
Completed 3 matchmade games of Warzone.
Completed 5 matchmade games of Strongholds.
Qualified for a Competitive Skill Rating.
Completed 5 matchmade games of Slayer.
Completed Mission 2.
Found and claimed a Skull.
Opened a Gold REQ Pack.
Completed Mission 1.
Completed any co-op Mission on Heroic difficulty.
Commanded your team of Spartans in Osiris.
Found and claimed one piece of Intel.
Called in a REQ that costs 5 Energy or more.
Changed your Spartan's gear in the Spartan Hub.
Changed your Emblem in the Spartan Hub.
Changed your Service Tag in the Spartan Hub.
Create and save a Custom Game.
Find and claim all Intel.
Finish Evacuation within 18:00 without dying on Heroic difficulty.
Find and claim all Skulls.
Escape the Hunters in the lab and fight them in the hangar in Blue Team.
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.
Escape the doomed Kraken by jumping onto a Phaeton piloted by a Spartan.
Knock two Hunters into the ocean during the Battle of Sunaion.
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.
Use a Ground Pound on an exterior power core in Guardians on Heroic difficulty.
Simultaneously destroy 2 cores in Guardians on Heroic difficulty.
Complete every co-op Mission on Heroic difficulty.
Complete a mission in Score Attack with at least 10,000 points.
Reach 50,000 points in Score Attack with a Skull multiplier of x2 or higher.
Complete a mission in Score Attack co-op, with all participants scoring at least 200,000 points.
Beat the par time of a mission in Score Attack.
Complete a mission in Score Attack with at least 500,000 points.
Earned a Mythic Boss Takedown in a Warzone Firefight match.
Successfully complete 5 Warzone Firefight matches.
Complete a Warzone Firefight match on 6 unique maps.