I'm designing a claw-based character with (among other things) the Girallon Arms soulmeld bound to arms (which gives me rend equal to claw damage + 1.5x strength) and the feats Rapidstrike and Improved Rapidstrike, which give me (unless I'm mistaken) 3 claw attacks with one claw and 1 with the other.
If I hit someone with all four attacks in a round, do I rend more than once? What if I hit one person with two claws and another with the other two claw attacks?
If you split your attacks between targets, hitting each twice, it seems clear at least in that case that you would get rend once on each target.
However, for the purposes of more rending on the same target by hitting that target more and more, the wording is really unclear and you’ll have to have to ask your DM.
The contention is this:
If you hit a single target with at least two claw attacks...
The at least wording implies that having more than two hits doesn’t trigger new rends... but it doesn’t really outright say so. Moreover, there’s no timing information given: when does that reset? I would guess that the intent is something like “if you hit a single target with at least two claw attacks during a single action,” or something similar, but it doesn’t say that. It could alternatively be a per-turn limit or per-round limit, or it could be something that can only happen in a full-attack (and then only once?). Taken literally, it seems like it would just be as soon as you got a second claw hit ever against a given target, you would get your first and only rend on that target ever, which seems wrong.
Anyway, I would ask your DM. My inclination is that it’s limited to once per action, and the two hits have to be scored during that one action (so a full-attack, or that feat that lets you attack with two weapons in an attack of opportunity, or whatever). Getting more than two claw attacks, e.g. with (Improved) Rapidstrike, doesn’t seem likely to help.
On the other hand, getting rend more than once hardly seems overpowered. Rend is a rare ability and it’s almost never available in large amounts. It rewards you for doing what you want to do anyway, so that could be appropriate as long as you don’t have to pay much to get it in the first place, but ultimately it’s pretty minor; not something you can really build a character around. Just a little cherry on top. If you want it to be more than that for your character, you might ask your DM to let you rend more (every two hits, every hit after the first, whatever) and argue that what you’re investing in getting rend is worth that much bonus damage. In my experience, this should hardly be game-breaking.
As this question isn't asking for RAW-only answers, mine will be:
It isn't explicitly stated in the rules, but from the description and ability name, Rend is made with two limbs simultaneously. And your build is trying to make second Rend with one limb. It is like if someone would try to stretch the rubber band with just one hand.
As a side note, if a creature has, for example, four claws, I'd let it make two Rends. One with first pair and another one with the second, no matter against one target or many. Still, even RAI hardly supports this last ruling.
If you successfully hit an opponent with both of the weapons you wield, you deal extra damage equal to [...]. You can gain this extra damage once per round against a given opponent.
So it is critical for the Rend to work to hit the target with two (or maybe more than two) weapons, not just two (or more) attacks.
To emulate your situation with the feat, let's say I have a guy of 11 level, with Two-Weapon Fighting and Two-Weapon Rend, with rapier and dagger. He has three attacks with rapier and one with dagger. And he can Rend only once, if his single dagger attack and at least one of his rapier attacks hit the same target.
Feat's mechanic may of cource be different from normal Rend, but it is useful if we are trying to lern the intent of the rules, or at least how CW authors understand them.
