Step 1: Stay around where Ysera is casting
Step 2: Death Grip or pull an enemy player near her
Step 3: Quickly kill the player, and jump into the Water
Step 4: Kill the Guards that pursue you. They are vastly weaker since Cataclysm, and a well-geared Tank or such, can easily slay them
Step 5: Killing these Guards now will roughly decrease 200 Reputation with the Guardians of Hyjal
Step 6: Have fun, as everyone in Mount Hyjal is now your enemy