Do multiple withering weapons penalties to AC stack with each other?

Question

Withering Weapon:

Property: Each time you hit with this weapon in melee, your target takes a cumulative –1 penalty to AC. The target can make a saving throw to end the entire penalty, but it can receive the penalty again with future attacks.

If I have two Withering weapons and I attack a target with twin-strike, what penalty is applied?

Case a) -2 AC (Save Ends)

Case B) -1 AC (Save Ends) -1 AC (Save Ends)

Case C) -1 AC (Save Ends)

Answer 1

Case B) is correct.

There are two nearly identical effects on the target, assuming you hit.

This question poses several interesting questions, I'll walk through the sequence giving my reasons.

• The primary hand hits with a withering weapon. The effect "-1 AC (Save ends)" goes to the target
• The secondary hand hits with a withering weapon.
  1. This does not increment the initial effect. Reason - The Withering Weapon clearly states that the cumulative effect is triggered "when you hit with this weapon" (emphasis mine).
  2. a second "-1 AC (Save ends)" is applied to the target.
• Should the second effect be ignored? Page 228 of the Rules Compendium tells us:

If a character is subject to identical effects that a save can end, ignore all but one of these effects.

It would certainly seem so. However this leads us directly into a conundrum. Next turn, when a withering weapon hits again, does it increment or not? It depends on which weapon did the last hit. We are instructed to ignore all but one, but which one did we keep, from the primary weapon or the secondary? As it matters, and we need to know this information, my ruling is that the effects are not identical and both must be retained and saved for separately.

• The only question left is what total AC penalty is applied to the unfortunate victim of two withering weapons. Page 29 of the Rules Compendium helps us here:

Penalties are added together, unless they're from the same named game element.

Withering weapon is a named game element and the penalties do not stack.

Answer 2

Case D) -1 AC (save ends) (save ends)

Multiple penalties usually stack, unless they come from the same named element. In that case only the worst applies.

In the same manner multiple auras from two exemplar of the same creature don't stack their penalties, so multiple instances of the same weapon property (even if applied from different weapons) don't. However, each effect carries its own save ends duration, so using two withering weapons helps in keeping the creature's AC at bay.

The creature is affected by the two eithering effects simultaneously. Each effect is kept separately, so they could independently increase their penalty; however, only the worst penalty applies.

       | Withering    | Withering    | Total Penalty 
ROUND  | Longsword    | Dagger       | to AC
----------------------------------------------------
1 hero | hit  (-1 AC) | miss         | -1
1 foe  |      fails   |              | -1
----------------------------------------------------
2 hero | hit  (-2 AC) | hit  (-1 AC) | -2
2 foe  |      saves   |      fails   | -1
----------------------------------------------------
3 hero | miss         | hit  (-2 AC) | -2
3 foe  |      fails   |      fails   | -2
----------------------------------------------------
4 hero | hit  (-1 AC) | hit  (-3 AC) | -3
4 foe  |      fails   |      saves   | -1

Each time the foe saves against one of the two effects, the penalty to AC caused by that effect resets.

I'd suggest to use two different dice to keep track of the independent AC penalties, removing the relative die each time the foe saves against that effect.