Valefor also has a second Overdirve that you can acquire once Yuna join the party. Return to Besaid and speak to the little girl with a dog standing next to the temple, and you'll receive an item that gives Valefor the Overdrive Energy Blast. If the little girl isn't near the temple, then look for her inside the item shop. Energy Blast inflicts greater damage at the cost of a higher recovery time.