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