How does the Titan Fighter's Giant Weapon Wielder ability work with Double weapons?
Giant Weapon Wielder (Ex)
At 1st level, a titan fighter can wield two-handed melee weapons intended for creatures one size category larger than himself, treating them as two-handed weapons. He takes an additional –2 penalty on attack rolls when using an over-sized two-handed weapon.
This ability replaces the fighter's 1st level bonus feat.
Double: You can use a double weapon to fight as if fighting with two weapons, but if you do, you incur all the normal attack penalties associated with fighting with two weapons, just as if you were using a one-handed weapon and a light weapon. You can choose to wield one end of a double weapon two-handed, but it cannot be used as a double weapon when wielded in this way—only one end of the weapon can be used in any given round.
Well, given that both a Taiaha (a 1-h double weapon) as well as more standard 2-h double weapons are all treated as one-handed+light for twf penalties, I'd say that the relative size of the weapon doesn't really affect how you fight double with it. Wielding a double weapon for TWF is still wielding a 2-h weapon; it's just that you treat it as a 1-h + light for the purpose of TWF penalties. So our Titan Fighter isn't "not" wielding a Large 2-h weapon just because he's wielding a Large Double Sword and two-weapon fighting with it as a double weapon, therefore Giant Weapon Wielder works just fine for it.
I understand how double weapons work.
It just seems like there is a bit of queer mechanics interaction, when used with this particular ability.
Such as, the additional -2, which stacks with size penalties, that is applied when the Titan Fighter uses his ability.
Does it apply when using the Full Attack action,to two-weapon fight?
I assume so, but, well, it's a queer case. I could be wrong.
I don't believe you can TWF with an oversized weapon in this way.
1. If you are wielding one end of a double weapon as a two-handed weapon, you can't use it as a double weapon (can't TWF).
2. If you are wielding it as a double weapon one end is a light weapon and the other is one-handed - it's not a two-handed weapon.
3. The Giant Weapon Wielder ability only works with 2-handed weapons.