When you critically strike with Searing Pain or Conflagrate, your Fire and Shadow spell damage is increased by X% for 10 sec.
Pyroclasm is a warlock talent which has a chance to increase fire and shadow spell damage for a short time.
Rank table
Rank
Spell power increase
1
2%
2
4%
3
6%
Patch changes
Patch 3.1.0 (14-Apr-2009): Re-designed: Now increases your Shadow and Fire spell power by 2/4/6% when you critically hit with Searing Pain or Conflagrate. Lasts 10 sec. Also moved down to tier 7, down from tier-5.
Patch 2.4.0 (25-Mar-2008): This talent now works correctly again with Rain of Fire.
Patch 1.9.0 (03-Jan-2006): The stun effect's duration no longer diminishes or is diminished by controlled stun abilities and spells (e.g. Cheap Shot, Hammer of Justice, Charge, etc).
Patch 1.8.0 (10-Oct-2005): Now gives a chance to stun when Rain of Fire, Hellfire, and Soul Fire spells damage the target.
Patch 3.1.0 (14-Apr-2009): Re-designed: Now increases your Shadow and Fire spell power by 2/4/6% when you critically hit with Searing Pain or Conflagrate. Lasts 10 sec. Also moved down to tier 7, down from tier-5. 
