Here is the full list of all 75 Halo Wars: Definitive Edition achievements worth 1,500 gamerscore.
Mission 11: Saved all the Airlocks.
100% Completion.
Mission 10: Distrupted all Tractor Beams.
Mission 8: Used Elephants to train 100 infantry.
Mission 4: Saved Adam.
Mission 3: Killed at least 5 Covenant Units with the Bridge.
Played Halo Wars for at least 24 Total hours.
Mission 2: Destroyed every Methane Tank.
Mission 1: Rammed and killed 50 Grunts with Warthogs.
Got a Scarab during a Reinforcement game.
Gained at Least 15 population from a single wave in a Reinforcement game.
Got 20,000 points in any Skirmish Game.
Finished with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Scored the winning point in a game of Keepaway against Legendary AI's.
Won a Skirmish Game with Dual Scarabs.
Killed 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Completed the Campaign on Legendary Difficulty.
Completed the Campaign on Heroic Difficulty.
Finished all missions under Par Time on Heroic difficulty.
Mission 7: Did not destroy any Power Node.
Mission 5: Jacked 6 Covenant Vehicles.
Finished five missions under Par Time on Heroic difficulty.
Obtained a lifetime campaign Score over 1,000,000.
Finished one mission under Par Time on Heroic difficulty.
Mission 14: Didn't claim an extra base.
Mission 12: Repaired the Power Core in less than 4 minutes.
Got a winning High Score with 10 or less Squads against the Heroic AI.
Won a Heroic Skirmish Game against the AI in under 10 minutes.
Hot dropped 50 squads to your Covenant Leader in a single game on Barrens.
Disrupted 5 active Leader Powers in a single game on Blood River.
Won a 3v3 Skirmish game with 2 AI Allies.
Got a Gold Medal with all Debuff Skulls Active.
Got a Gold Medal on every Campaign Mission.
Mission 6: Successfully protected every Rhino.
Improved your Score in any Campaign Mission.
Collected all Skulls.
Completed Mission 15 on any difficulty.
Mission 15: Opened the Doors in order.
Unlocked All Timeline Events.
Completed Mission 14 on any difficulty.
Completed Mission 13 on any difficulty.
Mission 13: Destroyed 25 units with the Scarab.
Completed Mission 12 on any difficulty.
Completed Mission 11 on any difficulty.
Completed Mission 10 on any difficulty.
Completed Mission 9 on any difficulty.
Mission 9: Every Colony put in Hibernation Mode at the same time.
Collected 8 Skulls.
Completed Mission 8 on any difficulty.
Completed Mission 7 on any difficulty.
Completed Mission 6 on any difficulty.
Completed Mission 5 on any difficulty.
Completed Mission 4 on any difficulty.
Completed Mission 3 on any difficulty.
Completed Mission 2 on any difficulty.
Collected your first Skull.
Got a Gold Medal on any mission.
Completed any Campaign Mission in Co-op Mode.
Completed Mission 1 on any difficulty.
Won 100 Skirmish or Multiplayer Matches.
Won 75 Skirmish or Multiplayer Matches.
Won 50 Skirmish or Multiplayer Matches.
Won 40 Skirmish or Multiplayer Matches.
Won 30 Skirmish or Multiplayer Matches
Won 20 Skirmish or Multiplayer Matches
Won a game on every Skirmish Map.
Unlock 20 Timeline Events.
Won 10 Skirmish or Multiplayer Matches
Won a Skirmish Game with every Leader.
Used one of the 6 Major Leader Powers to destroy an enemy's last unit.
Won a game in every Skirmish Game Mode.
Won and never trailed in a Tug of War game.
Unlocked a Timeline Event.
Won a Public game.
Won and had the highest score in a Public Game.