The The Only Traitor Add-on for The Final Station has 13 achievements worth 1,300 gamerscore.
Finish the game with Thomas.
Finish the game with a soldier.
Finish the game with an old friend.
Finish the game with Marc.
Finish the game with Charles.
Finish the game with Bob.
Finish the game with Matthew.
Finish the game with Brandon.
Finish the game with Bill.
Finish the game with Jesse.
Finish the game alone.
Finish the game with Harry.
Shoot a horse.