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