As an old friend of Carlisle Cullen, Siobhan (Lisa Howard) acts as the leader of the Irish vampires. She, like many of the new vampires in Breaking Dawn -- Part 2, has a special ability like Edward, Jasper and Alice. Her power -- though she doesn't believe she actually has it -- is the ability to manipulate a situation so it has the outcome she desires. This comes in handy when the Cullens and their vampire allies are forced to face off against the Volturi, the vampire royal family. Of all the powers that vampires can have, Siobhan's is considered one of the most powerful.