The Collected Works of Ambran the Seeker (3.5e Equipment)
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This mystical tome, filled to the brim with the collected notes, scribblings, and drawings of Ambran the Seeker -- one of the most famous paladins of Oghma -- grants its owner a +10 competence bonus on all Intelligence-linked skill checks in which they have at least 1 rank. The tome imparts this knowledge to its owner subconsciously; they need not reference the book manually each time they use these skills.
If they do decide to sit down and page through it, they can use the equivalence of the spell legend lore once per tenday even if they cannot normally cast spells. The amount of time needed to decipher the information they're after is equivalent to one-half the normal casting time of the spell (anywhere from 1d4×10 minutes to 2d6 weeks normally).
Corrupted: Unfortunately, these works fell into the hands of an evil lich many years ago who decided to add his own dark and twisted footnotes throughout. Forever corrupted, the tome is now considered a work of tainted evil. Any non-evil being who takes possession or reads from the tome suffers 1d6 points of Intelligence and Wisdom damage the moment they do so, and another 1 point of Intelligence and Wisdom damage every round thereafter. The book is not cursed, however, and may be dropped or relinquished at any time.