The Whittleton Creek Add-on for HITMAN 2 has 7 achievements worth 150 gamerscore.
Complete Another Life.
Eliminate Cassidy with laser wires, while fumigated, and take down Janus in a mole hole explosion.
Exit on a raft.
Complete all Mission Stories in Another Life.
Complete Another Life on Master Difficulty.
Select a Starting Location and use an Agency Pickup to smuggle an item into Whittleton Creek.
Reach Whittleton Creek Mastery Level 15.