Sinister Calling is a passive rogue ability learned at level 10 for those with the Subtlety specialization. It increases the rogue's agility.
Patch 6.0.2 (14-October-2014): Sinister Calling now increases Agility by 15% (down from 30%), and the amount of Multistrike bonus received from all sources by 5% (in order to act as Subtlety’s Secondary Stat Attunement). And finally, when the rogue Multistrikes with Backstab or Ambush, they also twist the blade, causing all Bleed effects to advance by 2 seconds, triggering an instant tick.
Patch 4.0.6 (8-Feb-2011): Sinister Calling now grants 30% Agility, up from 25%, and increases Backstab and Hemorrhage damage by an additional 40%, up from 25%.
Patch 3.1.0 (14-Apr-2009): The damage bonus to Backstab and Hemorrhage is now 2/4/6/8/10%, up from 1/2/3/4/5%.
Patch 2.4.3 (2008-07-15): Sinister Calling now increases damage to Backstab and Hemorrhage by 1/2/3/4/5% (down from 2/4/6/8/10%.)
Patch 2.3.2 (2008-01-08): Sinister Calling now also increases the percentage damage bonus of Hemorrhage and Backstab by 2/4/6/8/10%.