Enchantment, 1B (2) As Circle of Affliction comes into play, choose a color. Whenever a source of the chosen color deals damage to you, you may pay {1}. If you do, target player loses 1 life and you gain 1 life.1
Illus. Rob Alexander
This ability goes on the stack after you are damaged. If the damage reduces your life to zero, the game will end before this ability can resolve. [Planar Chaos FAQ 2006/12/13]
You can target a player to lose the life that is different from the player that controlled the source that damaged you. [Planar Chaos FAQ 2006/12/13]
If several sources deal damage to you at once (as in combat damage), this ability triggers once for each source. [Planar Chaos FAQ 2006/12/13]