Grimoires are special books found as loot that grant a bonus to spell damage specifically in PvM combat. These books cannot be crafted and must be obtained through various means. It's important to note that the bonus effects of Grimoires only apply during PvM encounters and do not affect spell damage in PvP situations.
Grimoires possess charges, representing the number of spells that can be cast using the book. Each spell cast will consume one charge from the Grimoire. To utilize its benefits, the Grimoire must be held in the character's hand and cannot be used while in another equipment slot.
Interestingly, Grimoires do not automatically unequip after casting a spell, allowing for continuous use without interruption. Initially, Grimoires are unidentified, but when used in their unidentified state, they function as if they were identified, revealing their true properties and effects.
The Grimoire is also used in the Skill Mastery: Resisting Spells