Pretty simple exploit to get +50% shadow damage as priest. It requires you to have a Holy offspec.
Step 1: Queue for a Skirmish Arena as Healer.
Step 2: Win the Arena as Holy with Chakra:Chastise on.
Step 3: Profit, you now have +50% Shadow damage until you die. You can zone with this.
Credit goes to this guy for posting it in another thread. Didn't realize it considering the thread name. http://www.ownedcore.com/forums/worl...ml#post3169622 (Boomkin form in Restoration / Guardian - Gamebreaking Bonuses)
Leaving it up for the sake of a more detailed explanation however.
https://i.imgur.com/VpzokRM.jpg