The Missions & Monsters Add-on for Fell Seal: Arbiter's Mark has 10 achievements worth 470 gamerscore.
Master all 22 Monster Variants
Master the 3 new Human Classes
Complete an encounter deploying only Monsters
Enlist each of the base 18 recruitable Monster types
Defeat an enemy with a Pet Effect
Complete all unique Hunts and large-scale battles
Complete all Missions
Fully upgrade all 5 regions
Complete 100% of Missions in one region
Build a Guild Upgrade