The Isle of Sgàil Add-on for HITMAN 2 has 7 achievements worth 150 gamerscore.
Complete The Ark Society.
Trap Zoe in the effigy, strangle Sophia with the necklace, force the Constant to come quietly.
Take the scenic route.
Complete all Mission Stories in The Ark Society.
Complete The Ark Society on Master Difficulty.
Select a Starting Location and use an Agency Pickup to smuggle an item into Isle of Sgàil.
Reach Isle of Sgàil Mastery Level 20.