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