Paizo PRD: Universal Monster Rules wrote:
Rend (Ex) If it hits with two or more natural attacks in 1 round, a creature with the rend special attack can cause tremendous damage by latching onto the opponent's body and tearing flesh. This attack deals an additional amount of damage, but no more than once per round. The type of attacks that must hit and the additional damage are included in the creature's description. The additional damage is usually equal to the damage caused by one of the attacks plus 1-1/2 the creature's Strength bonus.
Q: Is the damage from the rend special attack added as bonus damage to the attack that triggered the rend, or is it applied as a separate instance of damage from the triggering attack?
Follow-up QA: If it's applied separately, how is the damage type determined for the purpose of overcoming damage reduction and regeneration?
Follow-up QB: If it's added as bonus damage, how does the strength modifier to damage on the rend interact with the strength modifier to damage on the triggering attack (since this FAQ states these are both strength bonuses, and thus do not stack).
Previous threads relevant to the question:
Rend + Power Attack (1/3/2010)
Rend vs DR (4/29/2011)
Consensus on Rend vs DR (4/19/2015)
Unofficial responses:
James Jacobs has stated his opinion that rend is not a separate source of damage. (1/3/2010)
Mark Moreland has stated rend is a separate instance of damage and that power attack applies. (9/6/2012)
Mark Seifter has run it as a separate source of damage, but has stated the wording is ambiguous. (9/23/2015)
Supplemental:
The stat blocks for the Troll Ripper, Render, and Monarch from Monster Codex illustrate that rend does not receive bonuses to damage as claws do (receiving no benefit from the Amulet of Mighty Fists nor Weapon Training: Natural), except when otherwise noted (such as with rending gauntlets). This seems to be in conflict with Mark Moreland's interpretation. (As an aside, the rend damage on the Troll Fury and Elder Matron seem to be in error, with their rend damage not being adjusted for their slightly higher and lower strength modifiers compared to the bestiary troll.)
Improved Rending Fury adds damage to a rend, but mentions that damage not multiplying on a critical hit. Its Combat Trick allows the damage to multiply on a critical hit. Neither are possible unless rend damage is added to an attack.
So if you'd like to see an answer, hit the FAQ button! Thanks!
