If anyone could glance over this and let me know if they spot any problems, I would appreciate it.
Taddol race with the Monstrous Physique (talent) feat with the Titan Mauler Barbarian archetype and the Abyssal Blood rage power, dual wielding two Earth Breakers with the Impact weapon property.
The Taddol race has the Superior Two-Weapon Fighting feat which says in part, "You do not take a penalty on attack rolls for fighting with two weapons."
Each head can control a melee attack independently, eliminating penalties for attacking with a weapon in each hand.
Prerequisite: Taddol, Big Hands, Two-Weapon Fighting
Benefit: You do not take a penalty on attack rolls for fighting with two weapons.
Combined with the Titan Mauler's Jotungrip ability to wield a two-handed weapon in one hand...
...and the Monstrous Physique talent that increases my size category by one...
You are an unusually big specimen of your race.
Prerequisite: Con 13, Str 13, character level 1st
Benefit: Increase your size category by one, apply the size advancements for reach, armor class, and attack rolls; do not apply the remaining normal size advancements, such as Strength and Constitution increases.
...and the Abyssal Blood rage power that also increases my size by one while I rage...
Prerequisite(s): Barbarian 10, abyssal blood (lesser)
Benefit(s): Once per day when the barbarian enters a rage, she can choose to grow one size category larger than her base size (as enlarge person, even if the barbarian isn't humanoid).
...and finally the Impact weapon property that treats my weapon damage as though it were one size larger...
So, after I qualify for all the feats, abilities, rage power, etc., and can afford two Earth Breakers with the Impact property, this is what I get:
While raging, once per day, I will be Huge size (Monstrous Physique + Abyssal Blood) wielding two Huge Earth Breakers that do damage as though they were Gargantuan sized, and only be taking a -2 penalty to my attacks with each weapon (from the Jotungrip ability; the Superior Two-Weapon Fighting negates the two-weapon fighting penalties).
A Medium Earth Breaker does 2d6 damage. If my weapon progression is correct (as per the progression listed under the Improved Natural Attack feat, which is the only weapon progression that I can find that goes high enough), a Large Earth Breaker does 3d6 damage, a Huge Earth breaker does 4d6 damage, and a Gargantuan Earth Breaker does 6d6 damage.
Does all this look right?
Monstrous Physique states what the increased size applies to and that it does not affect the rest. Size of weapons wielded is not called out to increase.
The natural weapon damage chart is different to the manufactured weapon chart. So it might be wrong.
And apart from that it uses 3pp stuff that a lot of GMs do not allow.
Just looking over the race told me that it is rather ridiculous.
Absolutely wouldn't allow that race at all. I've seen it before, and its so fraking overpowered it's not even funny.
Also, multiple polymorph effects don't stack, and neither do effects that increase your size stack with polymorph effects either. See the polymorph rules in the Magic Chapter of the Core rulebook.
Therefore monstrous physique and abyssal blood will not stack, because abyssal blood works like Enlarge Person.