Do racial natural attacks matter for a Synthesist's attack limit?

Question

Synthesists are a unique summoner archetype that combines with the eidolon, which can range from a Hulk or werewolf relationship to powered-up final forms, to a super-suit. The eidolon is a separate creature by the rules, but the summoner wears the eidolon.

A synthesist eidolon does not get its own feats, but the hybrid gets to use the feats of the summoner generally. Eidolons do have a limit on the number of natural attacks they may have. My question is how a synthesist would handle having a natural attack from race, feat, or class feature? For the sake of an example, Eldritch Heritage with the Serpentine Bloodline:

Serpent’s Fang (Ex): At 1st level, you can grow fangs as a free action. These fangs are treated as a natural weapon inflicting 1d4 points of damage plus your Strength modifier (1d3 if you are Small) plus poison (Bite—injury; save Fort DC 10 + 1/2 your sorcerer level + your Constitution modifier; frequency 1/round for 6 rounds; effect 1 Con damage; cure 1 save).

This seems like a good test as the feat gives the ability to grow the fangs. A second scenario to consider would be a race with natural weapons. Would these natural attacks of the summoner be:

A) Included as part of the eidolon and so counted against the limit.

B) Not accessible as they are natural attacks of the summoner rather than the eidolon.

C) Available to the eidolon, but not considered for the limit.

Ultimately such a case is up to the DM of a game and such oddities are a contributing factor for why the synthesist has always been banned for PFS, but I have always been a firm believer in trying to understand something like this before springing it on a DM. Thematic-wise, I would think racial natural attacks that always exist would fit under B, while the ability to grow them would fit under A or C depending on whether ruling for balance or thematics respectively, but I may be missing a rule along the way.

Answer 1

You are limited by the Maximum Attacks value

This has been answered in a FAQ:

Summoner: Can a synthesist (page 80) make attacks from his own body (such as manufactured weapons, unarmed strikes, or natural attacks) and attacks from the fused eidolon in the same round?

Yes, but the fused character's natural attacks are still subject to the Maximum Attacks entry in the table for an eidolon of his level. For example, a 1st-level synthesist is limited to 3 natural attacks per round, whether those natural attacks are from the eidolon, the synthesist, or a combination of the two.

If the synthesist wants to use his eidolon's natural attacks and use his own manufactured weapons or natural weapons in the same round, his eidolon needs to have enough limbs to account for all of these attacks. For example, a gnome synthesist fused with a two-armed biped eidolon has two arms it can use to make attacks; if the synthesist wants to make claw attacks with his eidolon's claws and also make weapon attacks (such as with a dagger or staff), he needs to give his eidolon additional arms evolutions to hold those weapons (as an extension of the summoner's own limbs)--a two-armed eidolon can't make two claw attacks and also make a dagger attack or staff attack in the same round.

Remember that the synthesist is still subject to the rules of combining manufactured weapon attacks and natural weapon attacks in the same round (in that the natural weapons are always considered secondary and therefore have a -5 attack penalty).

Remember also that the summoner is wearing the eidolon like a biological, all-encompassing "suit," and the eidolon's shape limits what the summoner can do. If the eidolon doesn't have arms, the summoner can't use his own arms to manipulate objects, make attacks, cast somatic spells, or anything else requiring arms--while fused, the summoner's limbs are trapped within the armless eidolon-suit, and he isn't able to use them to manipulate things. The summoner isn't able to extend his own body parts outside of the eidolon-suit; if he wants to be able to manipulate things with arms, the eidolon needs arms (though tentacles are sufficient for simple tasks).

(Note: It is a matter of flavor and player's preference whether the synthesist floats immobile within the eidolon-suit and its limbs move at his mental command, if the synthesist moves his own arms and the eidolon-suit's arms echo this movement, or if the eidolon-suit is more form-fitting and the flesh-enveloping limbs move in direct response to the synthesist's own movements.)

Note: This clarifies an earlier FAQ error where the summoner's weapon attacks counted toward the number of attacks on the table.

The Syntethist is a complicated archetype and you should take a read of the multiple FAQs released about it before proceeding. Otherwise, you will come up with many questions already asked about them. Being written poorly as it was (due to word count, apparently), it is no wonder that those questions pop up frequently.