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