How does BAB Breakdown for an Eidolon with Multiple Natural Weapons

Question

I'm trying to figure out how my Quadrapedal Eidolon attacks per turn break down BAB-wise since I've never used the Summoner previously. (Evolutions Below specifically).

It came with a Bite and Claw evolution as a Qped and I've added another Claw evolution giving it 2 Sets of Claws and a potential bite. At level 12 Eidolon has 5 Max Attacks. I'm trying to wrap my head around how I would pace a turn with the Eidolon. currently, at Lv12 it has a BAB of 9/4, I see that an Eidolon can make a potential Max of 5 Attacks.

How does that roll out dice-wise with BAB and the Natural Weapons? If my Eidolon were to Declare a Full Attack against a target: What attacks are rolled at Full BAB and what attacks would be rolled at the half BAB of 4? As I see it now I would make 1 Claw Attack at a +9, and 1 Claw at a +4 would I make the other 2 Claws and the Bite at the +4 or with No Attack Bonus?

I do understand that every 2 Successful Claw attacks proc a Rend roll and every successful attack procs Energy Attack (Acid) so I get that.. but I am unsure about how I would roll out the Max 5 Attacks in play.

Evolutions:
Pounce: 1
Claws (2): 2
Spell Resistance: 4
Large: 4
Rend: 2
Energy Attacks (Acid[1d6]): 2
Improved Damage: 1

Answer 1

Natural attacks don't work the same way BAB-based weapon attacks do.

Natural Attacks

Most creatures possess one or more natural attacks (attacks made without a weapon). These attacks fall into one of two categories, primary and secondary attacks. Primary attacks are made using the creature’s full base attack bonus and add the creature’s full Strength bonus on damage rolls. Secondary attacks are made using the creature’s base attack bonus –5 and add only 1/2 the creature’s Strength bonus on damage rolls. If a creature has only one natural attack, it is always made using the creature’s full base attack bonus and adds 1-1/2 times the creature’s Strength bonus on damage rolls. This increase does not apply if the creature has multiple attacks but only takes one. If a creature has only one type of attack, but has multiple attacks per round, that attack is treated as a primary attack, regardless of its type. You do not receive additional natural attacks for a high base attack bonus. Instead, you receive additional attack rolls for multiple limb and body parts capable of making the attack (as noted by the race or ability that grants the attacks).

TL;DR you refer to a table and find out which natural attacks are primary or secondary, and treat them differently based on that.

Bite and Claw are both Primary attacks. If you have 1 bite attack and 4 claw attacks, your attack routine is bite/claw/claw/claw/claw, so 5 attacks, all using 9 bab (+ whatever bonuses) and adding your full strength modifier to damage (instead of half). Both the Bite and Claw evolutions specify that these are primary attacks, to avoid any confusion from the tables or monster creation rules.

However.

The claws evolution states that you can only have one set of claws on legs. Ergo you'll need your eidolon to have a pair of arms, to take it twice.

Answer 2

For all creatures:

• Primary natural weapons attack at full BAB. They also add the creature’s full Strength modifier to damage (or 1½×Str if the weapon is the creature’s only natural weapon, or if the weapon says so).

• Secondary natural weapons attack at full BAB − 5; not half BAB as you thought. They also add only half a Strength bonus to damage (a Strength penalty is still added in full).

These do not interact with each other in any way: a natural weapon is either primary or secondary, and that’s the end of the discussion when dealing with just natural weapons.¹ BAB has zero effect on natural weapon attacks beyond simply being a number you add to your d20 roll when you make an attack—you do not get more natural weapon attacks for high BAB (so the “/+4” part of your eidolon’s +9/+4 BAB only matters if the eidolon uses a manufactured weapon; for natural weapons alone only the +9 matters).

Note that many natural weapons require the appropriate body part in order to be effective: you can’t use two bites unless you have two heads, you can’t use four claws unless you have four limbs that can use claws, etc.

Again, all of the above is for all creatures.

The only complication that eidolons introduce is the maximum attacks limit. This limits the evolutions you may select, however; it doesn’t technically affect full-attacks except via influencing the evolutions that the eidolon can have. If someone cast a spell on your eidolon that gave it more natural weapons, over the 5 that its evolutions grant, it would be able to full-attack and use those new natural weapons in addition to the 5 from evolutions.

So your bite and claws are primary, and use full BAB, i.e. +9 (plus bonuses from Strength etc.), and add the eidolon’s full Strength bonus to damage.

However, note that—contrary to what you say in the question—quadruped eidolons only start with a bite. You have to use evolutions to add claws. And you can only add the claws evolution to one pair of legs, so you have to add arms in order to add your second pair of claws.

1. _{All natural weapons are downgraded to secondary when used in the same full-attack as manufactured weapons.}