Spelltouched

Base Mechanic
This hidden effect can be found on throwing weapons from the Eveningstar Challenge Pack. Basically it creates a random second thrower of the same tier / minimum level for one throw. (This means a ML16 or ML20 thrower actually has six abilities, though three of these are totally random. A ML24 thrower has eight abilities, four of which are totally random.)

Test 1: Common procs
Setup:
 * Sample size: 66 hits
 * Testing aim: What common additional abilities are added on average.
 * Testing target: The red named giant in The Tracker's Trap on epic normal.

Result:
 * nothing: 1
 * 2d6/burst bonus damage: 23
 * 1 stat damage and 2d6 or burst bonus damage: 31
 * 1 stat damage: 3
 * Improved Destruction and 2d6/burst bonus damage: 2
 * 2d6 untyped and 2d6/burst and 1 stat damage: 5
 * 2d6 untyped and 2d6/burst bonus damage: 1

Conclusion:
 * Since only 4 times no 2d6/burst bonus damage occurs, it can be safely assumed that those were evil/anarchic damage procs which did not show up in combat log.
 * Thus a spelltouched thrower can be expected to have the following common procs:
 * Always either 2d6 bonus damage or a burst type bonus damage (elemental, alignment, force or light)
 * A ~59% (probably 60%) chance for one random ability damage (strength, constitution or dexterity)
 * A ~9% chance for 2d6 untyped damage (Hemorrhaging)
 * A ~3% chance for a random debuff (Improved Destruction or Improved Shattermantle)

Test 2: Rare procs
Setup:
 * Sample size: 1000 hits
 * Testing aim: What average additional damage can be expected from rare procs.
 * Testing target: Training Dummy.

Result:

Conclusion
 * The average additional damage per hit, that can be expected from rare procs, is around 5,9 damage.

Conclusion
Both tests combined show that the average expected damage per hit is about 12,5 within an error of about ± 0,5 damage/hit (also depending on targets alignment)