How does Stand Still and Two-Weapon Rend work together?

Question

Stand Still [General]

You can prevent foes from fleeing or closing.

Prerequisite

Str 13.

Benefit

When a foe’s movement out of a square you threaten grants you an attack of opportunity, you can give up that attack and instead attempt to stop your foe in his tracks. Make your attack of opportunity normally. If you hit your foe, he must succeed on a Reflex save against a DC of 10 + your damage roll (the opponent does not actually take damage), or immediately halt as if he had used up his move actions for the round.

Since you use the Stand Still feat in place of your attack of opportunity, you can do so only a number of times per round equal to the number of times per round you could make an attack of opportunity (normally just one).

Normal

Attacks of opportunity cannot halt your foes in their tracks.

When using the feat Double Hit, the character can hit the opponent with two weapons (rather than one) in an AoO.

When both weapons hit, it could trigger Two-Weapon Rend and cause extra damage.

Would all 3 damage rolls be added together for the DC calculation, or would the opponent get 3 different checks for using Stand Still?

Answer 1

Rend effects are really weird, because it’s not clear which damage roll they get added to, and sometimes they seem like they might be a separate damage roll altogether.

Two-Weapon Rend is gives a bit of a hint, though.

When making an attack of opportunity, you may make an attack with your off hand against the same target at the same time.

^{(Double Hit feat benefit, Miniatures Handbook pg. 25)}

This makes it pretty clear that there is the (main-hand, presumably) attack of opportunity, and then there is—separate from that—an off-hand attack. The off-hand attack is not described as an attack of opportunity.

Thus, you can use Stand Still, and it will replace the main-hand attack with the Stand Still effect, and you’ll still get the off-hand attack. This is good, in one sense, because you’re still dealing some damage, but it doesn’t make your Stand Still effect any better: the DC is still based on the damage your one attack of opportunity isn’t doing, and doesn’t factor the second attack in at all.

If you successfully hit an opponent with both of the weapons you wield, you deal extra damage equal to 1d6 + 1½ times your Strength bonus.

^{(Two-Weapon Rend feat benefit, Player’s Handbook II pg. 84)}

Here we have “extra” damage, but it’s not clear which “bucket” it’s going into—the attack of opportunity damage, the off-hand attack damage, or a third, separate thing. It only counts for Stand Still if it adds to the attack of opportunity damage (and thus will not actually deal that damage and instead increase Stand Still’s DC).

However,

This extra damage is treated as the same type that your off-hand weapon deals normally for the purpose of overcoming damage reduction and other effects related to damage type.

^{(Two-Weapon Rend feat benefit, Player’s Handbook II pg. 84)}

This hints somewhat strongly that the extra damage from Two-Weapon Rend is not being added to your main-hand attack damage—and that’s the one that is the attack of opportunity, whose would-be damage is used to calculate Stand Still’s DC. It’s not impossible, of course, that it is, but it doesn’t seem likely, considering that the damage type is explicitly the same as the off-hand weapon, instead.