This will unlock on the last mission done for the midget guy. HUGE TIP: When the Graug starts feasting on Ghuls, don't waste any of your arrows by shooting the Graug. Instead, start killing all the Ghuls that are gathering around the Graug (if you have the STORM OF URFAEL or SHADOW OF ACHARN attribute unlocked, this part would go very fast). After you've killed all the Ghuls, the Graug will charge at you and then you have to quickly shoot him in the head and dodge. Keep doing this and he'll be dead soon. After that, enjoy the epic cutscene and your reward, the achievement :)