Blasters' earliest abilities come so naturally to them, that they are accessible even in states that normally prevent them from using powers, such as being Held, Slept or Stunned. Additionally, each time the Blaster attacks with a primary or secondary power, they gain a stacking damage bonus for the next several seconds. The amount of the damage bonus and its duration is dependent on the exact power used, with single target abilities generally giving the largest bonus.
Even while a Blaster is mezzed, he can use the first two powers of his Primary power set and the first power of his Secondary power set. There is a stacking damage bonus for any attacks used from either set the effectiveness of which varies per power.
Castle gave the following formulas for Defiance's damage bonuses during beta testing. Some exceptions have been found, but the formulas are reliable for the most part. Also, for snipes, Activation Time does not include the interruptible period.
Duration = 7.5 + Activation Time
Each bonus starts when an attack begins to activate and lasts throughout the activation, plus 7.5 seconds more. So every attack provides the same window afterward for additional attacks to get its Defiance bonus.
Damage Bonus = 6.6% * Activation Time / Area Modifier where Area Modifier = 1 + (0.15 * radius) - ( 0.0003667 * radius * (360 - arc) )
This means that attacks with long activations give bigger Defiance bonuses than quick attacks do, and single-target attacks give bigger bonuses than small AoEs, which give bigger bonuses than large AoEs.
(Notice that Area Modifier is always just 1 for single-target powers and always 1 + (0.15 * radius) for circular AoEs. You only need the whole formula for cones.)
Defiance was changed to its current state on December 11, 2007. The previous version, introduced in Issue 5, made use of the "brown bar" on the UI, which represented a buff to Damage and ToHit. As a Blaster's HP dropped, Defiance's buff would rise. The exact mathematical forumlas used to calculate new Damage and ToHit values are as follows:
Multiplier = 2 ^ ((45 - HealthPercentage) / 10) DamageBoost = 25% * Multiplier ToHitBoost = 1.25% * Multiplier
Following that route, the buff values at 25% health would yield a 100% boost to Damage and a 5% boost to ToHit. At 5% health, there would be a 400% boost to Damage and a 20% boost to ToHit.