In an upcoming Pathfinder campaign, one of my friends that loves to attempt to break games is about to take the Summoner class. Out of caution and curiosity, I looked through the advanced evolutions that his character could purchase and got stuck on Limbs as shown around the middle of this page. The major problem with the rules written as they are is that they give a static BAB for the creature without additional attacks (aside form natural attacks), set a rule where each pair of arms needs an evolution for either a natural attack or an overall weapon profeciency in order to use them in battle, but completely neglect to mention how extra arms wielding weapons work.
In the end, I would like to know this:
Does having extra limbs give the Eidolon additional weapon attacks, or does it just give it weapon options in a battle without the risk of invoking attacks of opprotunity?
Best Answer
The Multi-Weapon Fighting Feat, has the answers you need.
The 'normal' entry is the only place in the SRD that I can find where fighting with more than two hands and more than two weapons is covered. The Two-Weapon Fighting entry in the Combat section is short and refers only to wielding two weapons at once.
Extra attacks from BAB are not the same as extra attacks that you get from wielding a second (or third) weapon. Those apply even if you are multi-wielding (ergo, a 7th level fighter with 4 arms wielding four shortswords with the Multi-Weapon Fighting feat would have 5 attacks - 4 from multi-wielding, calculated using a base attack bonus of 7, and then another from high-BAB, on his primary hand, calculated using a base attack bonus of 2 (7 - 5)).
Notably, the eidolon's limitation on natural attacks by RAW does not apply to manufactured weapons, and natural weapons can be used as 'secondary natural attacks' (-5 to hit, 1/2 str bonus to damage) even if your main attack routine is with a manufactured weapon.