Spontaneous Spell, Variant (3.5e Feat)
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Spontaneous Spell [Metamagic]
You can sacrifice a prepared spell to cast an unprepared spell.
Prerequisite: Ability to cast prepared spells, Caster Level 6th.
Benefit: As a swift action, you can swap out any currently prepared spell for any other spell on your spell list (or spell book for a wizard) as if changing which spells you have prepared for the day. However, the spell you sacrifice must be two spell levels higher than the one you prepare.