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