Asmodian avatars at level 10 or higher will receive Berdin's Amulets, which grant 50% more XP from hunting, gathering, and crafting for a period of one hour (with a one-hour cooldown period after activation). Gateway Getaway events will also happen more frequently, and Asmodian characters will be granted entry to Abyss instances despite Elyos ownership of the forts.
Finally, fortress siege incentives will be handed out on a weekly basis, with additional medals being awarded based on which forts are conquered. In short, there's never been a better time to roll an Asmodian alt or convince your friends to join you on Aion's dark side. Head to the official web site for more info.