Sigil of Power

Source
This item drops from all raid boss encounters as personal loot in Mogu'shan Vaults, Heart of Fear, Terrace of the Endless Spring, Throne of Thunder or the eight first bosses in Siege of Orgrimmar. The sigils will drop in all four raid modes: Raid Finder, Flexible (for Siege of Orgrimmar), 10/25-player Normal, and 10/25-player Heroic. The chance for the item to drop is one attempt per eligible boss, per week across all difficulties, and the chance for the item to drop is the same regardless of difficulty mode. Lei Shen and the Sha of Pride have a 100% drop rate.

Objective of

 * The Strength of One's Foes