The Alien Hunters Add-on for XCOM 2 has 10 achievements.
Use all ruler armor abilities in a single mission
Kill the Archon Ruler
Kill all alien rulers in a single game
Use a ruler armor ability against an alien ruler
Purchase all of the final tier Hunter Weapons
Kill an alien ruler the first time you encounter it
Kill the Berserker Ruler
Kill the Viper Ruler
Investigate the Abandoned Research Facility
Kill an alien ruler while it attempts to escape