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Burning Spell (Metamagic)
You cause creatures to take extra damage when you affect them with a spell that has the acid or fire descriptor.
Benefit: The acid or fire effects of the affected spell adhere to the creature, causing more damage the next round. When a creature takes acid or fire damage from the affected spell, that creature takes damage equal to 2× the spell's actual level at the start of its next turn. The damage is acid or fire, as determined by the spell's descriptor. If a burning spell has both the fire and acid descriptor, the caster chooses what kind of damage is dealt by the burning spell effect. A burning spell uses up a slot two levels higher than the spell's actual level.