The Sergeant Johnson Leader Add-on for Halo Wars 2 has 3 achievements worth 30 gamerscore.
Use Repair Beacon special ability 15 times. (Multiplayer, Skirmish or Blitz)
Win 3 matches as Sgt. Johnson (Multiplayer, Skirmish or Blitz)
Kill 50 infantry units with the Colossus' Stomp ability (Multiplayer, Skirmish or Blitz)