The Mark of the Assassin Add-on for Dragon Age II has 5 achievements worth 120 gamerscore.
Defeat Duke Prosper, with or without Tallis.
Disarm the fire traps in Chateau Haine's vaults.
Evade vault security in Chateau Haine.
Lure and kill an alpha wyvern near Chateau Haine.
Meet Tallis in Hightown.