The The Arbiter Leader Add-on for Halo Wars 2 has 3 achievements worth 30 gamerscore.
Win 3 matches as The Arbiter (Multiplayer, Skirmish or Blitz)
Kill 20 air units with the Arbiter while raging (Multiplayer, Skirmish, or Blitz)
Trap 100 units with Stasis (Multiplayer, Skirmish, or Blitz)