The Bloody Thorns are a terrorist organization whose aim is topple the governments of the world and return the world to the only truly fair state, chaos. Their name is derived from both the identifying symbol they carry on tiles and the test which they must endure in order to become fully fledged members.
It is relatively easy to tell the difference between an initiate and a full fledge member of the order, only those who are deemed worthy are allowed to take the test and prove their will. Those who have bear the scars around their head from the crowns of thorns they were bound with for 7 days, as well as around their wrists and ankles. These living thorn vines bind their targets tighter and tigher as they days go on. Any begging for release or death is seen as a sign of weakness and the initiate is killed on the spot.
Few are willing to endure such torture, but those who do have wills of iron and the power to command any and all intiates to do anything they ask. As all members are benders these ordeals push the bending of those who go through them to terrifying new heights.
(Image used was found under an anonymous posting online. Image shall be removed upon request)