Class Pet (3.5e Feat)
From D&D Wiki
Class Pet [Ability Swap, Arcane]
You learned that your winning personalty and good looks can get you passing grades in magic school. You slowly have learned magic and can cast using your force of personality.
Prerequisite: This feat must be taken at character creation
Benefit: Use your Charisma in place of Intelligence for learning, preparing, and casting spells. Bonus spells are determined by your Charisma, as is the amount of spells in your spell book at first level. Spell save DC that would be based on Intelligence are instead based off of Charisma.
Normal: Learning, preparing, casting spells, bonus spells, the amount of spells you gain at first level, and spell save DC use Intelligence.
Special: When you prepare your spells, if your Intelligence score is less then that required to cast the level of the spell (Int - 10), then memorizing the spell takes twice as long.