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