Cursed Luck has a 50% chance to add a negative drn to the bearer's Defence and Protection rolls. Why is it all lowercase? Because, fortunately for the bearer, only one six-sided die is used as the base for this effect; regular DRNs use two.

Cursed Luck can, in fact, bring a fellow below the traditional minimum result for rolling a DRN (or even a regular 2d6). It thus increases the chance of being critically hit more than you might think, since it adds two potential values (zero and 1) for getting critically hit. It cannot make the result negative, however; the minimum is zero. Out of 1296 Cursed Luck DRNs, around 490 will be 2 or lower, around 625 will be 3 or lower, and around 758 will be 4 or lower. For 1296 regular DRNs, 36 will be 2's, 108 will be 3 or lower, and 216 will be 4 or lower. Thus:

• Against most units with Cursed Luck, around 20.29% of all hits (~13/64) will be armor-defeating.
• Against units with Cursed Luck and 50-99 Fatigue, around 28.29% of all hits (~9/32) will be armor-defeating.
• Against helpless/entrapped units with Cursed Luck, around 37.58% of all hits (~3/8) will be armor-defeating.

The average result of a DRN is an 8. The average result of a Cursed Luck DRN is around 4.25, so Cursed Luck effectively:

• Reduces Defense Skill for melee attacks, and possibly the Shield Parry in missile combat, by an average of 1.875
• Increases Armor-Negating Damage on them by an average of 1.875
  • Due to critical hits, this increase is higher for hits that respect Protection, though never enough to out-scale Protection.
  • For a person with 10 max HP, this also means each AN hit is around 18.75% more likely to cause an Affliction!

Does the effect apply to anything else? Perhaps. The public information on this is two games out-of-date.

Fateweaving is the most common source of this thing; attackers of Fateweavers, if their attempts aren't stopped by Petrification, Awe, or Vine Shield shenanigans, have their Luck cursed if they fail a Magic Resistance check versus the indicated value.

Cursed Luck negates Luck! Luck gives a fallback 75% chance to not take damage from hits that would kill, as long as they aren't instakills. Cursed Luck shuts this lifesaving ability off completely.