Master Poisoner is a passive core rogue ability learned at level 64. It grants increased spell damage against poisoned targets.
Patch 3.3.3 (2010-03-23): Now correctly reduces the duration of a sting refreshed by Chimera Shot.
Patch 3.2.2 (2009-09-22): No longer increases the Deadly Poison application rate following a successful Envenom and instead now provides a 33/66/100% chance of preventing Envenom from consuming Deadly Poison.
Patch 3.1.0 (14-Apr-2009): Now also increases the bonus to apply Deadly Poison when Envenom is used by an additional 15/30/45%.