The Fell Grimoire is a tome containing dark magic secrets from the ancient Tevinter Imperium. According to a legend, the book holds the key for summoning powerful demons known as The Forbidden Ones.[1]
Involvement[]
After destroying the first five tomes for the quest Forbidden Knowledge in Dragon Age II, the Fell Grimoire can be found in the Forgotten Lair, which is a cave in Darktown next to the entrance.
Upon the tome's destruction, you will meet one of the most dangerous bosses in the game, Xebenkeck, a powerful desire demon. Defeating it grants the Exorcist achievement.
Destroying the Fell Grimoire also gives 
Merrill: rivalry (+10) if she is in the party, as with the other tomes.