The Sage's Wisdom is a consumable Item that sets the user's intelligence to 99 for one combat. This makes Spells extremely accurate and powerful, so it is well worth using during a tough boss fight.
The IntelligenceAbility, which powers the Sage's WisdomItem, simply sets the target's intelligence to 99 for the rest of the combat. It and the similar SpiritAbility are the only Abilities used at level 0, since level is irrelevant to the effect.