So, for two feats, you've netted an average +4 damage per hit. That seems comparable to other two-feat combos. Enlarge person or expansion could alter that further...
Where do these two feats come from? I've never heard of them.
Damage by size category increase is actually easier to pump with natural attacks than it is with weapons, believe it or not.
That said, my experience has been that this is a better way to start an argument than it is to fight. A lot of what pumps weapon size boosting into its final few stages take actions from your combat- and if your games aren't strict dungeon crawls, gigantic weaponry is usually obnoxiously hard to rationalize everywhere. Meaning, some fights happen without it.
Are you a GM or a player? Your first post sounded like a player, but now it sounds like you are GM, proposing a new rule. (If you are a player, be aware, players proposing new rules can be considered rude or greedy if it isn't fixing a problem for the group as a whole)
Having reach but not treating it as threatened space is really, really weird. Only thing I can think of that does that is the Whip, and that is because it is treated as a ranged weapon that isn't thrown.
Reach is a big deal, and while not threatening takes some of that away, it's still powerful- especially on a martial character.
That, and anything granting 10+ foot reach that isn't able to coil back up somehow is going to cause some problems with picturing what space you occupy (if you don't grow bigger than 5' in the process). If you've ever moved furniture, you should see why.
Someone that's 15 feet tall usually has some reach of their own. I think you might also find that this rule will also play havoc with a lot of the combat assumptions in the modules, especially if the PCs start using it to their advantage.
You are familiar with the Reach quality? Even swinging weapons, such as the Lucerne hammer, don't get to be used on adjacent enemies if they have Reach, and if you picture it for a bit, you can see why. So if you want to have a Medium sized character using a weapon that deals damage as though it were size categories bigger, I would suggest just making an impossibly heavy and robust version that is only awkwardly big, not one that will raise friendly fire questions.
Edit: And on a strictly legalese reading of the Powerful Build trait paraphrased above, Powerful Build doesn't change the extra effort needed to wield the weapon, just removes the penalty involved with attacking with it. So with the feats, you could use a Huge one-handed weapon or a Large two-handed weapon, but you couldn't go Huge two-handed weapon. (Maybe if you were a four-armed race with Powerful Build, but there are better things to do as a martial with four arms!)
Jotungrip specifies the weapon must be appropriately sized for you, so no-go on that. Massive Weapons does nothing to the effort, just the attack penalty. So, you are still kind of stuck in that regard.
No, because Powerful Build doesn't do anything to the "handedness" aspect either (which I had been calling "effort"). It just negates the attack penalty exactly like Massive Weapons does. In fact, if you have one of those two abilities, you don't need the other- they do the same thing. (Edit: Powerful Build does more in general, but Massive Weapons can negate the penalty for even bigger weapons. Neither affects handedness increases, though.)
So what you COULD do as a Half Giant with Lighten Weapon:
Gargantuan Dagger as a 2 handed weapon
Huge Dagger as a 1 handed weapon
Large Dagger as a light weapon
Huge Longsword as a 2 handed weapon
Large Longsword as a 1 handed weapon
Large Greatsword as a 2 handed weapon
If you really want to use big weapons: Rite Publishing has several PDFs with races that are Large size category or have racial classes that let them grow bigger. Ironborn, Giants, and Minotaurs are some examples. Then find some way to give the character the spells Lead Blades and Enlarge Person, make the weapon out of Alchemical Gold/Platinum (3.5), and give them the feats you point out plus proficiency in the material (3.5).
Also, if you are the DM, it's your game to run however you like. You can toss out the rules you don't like. Have fun at the core of it all.
Massive Weapons (Ex): At 3rd level, a titan mauler becomes skilled in the use of massive weapons looted from her titanic foes. The attack roll penalty for using weapons too large for her size is reduced by 1, and this reduction increases by 1 for every three levels beyond 3rd (to a minimum of 0). This ability replaces trap sense.
Powerful Build: ...A half-giant can use weapons designed for a creature one size larger without penalty.
Massive Weapons describes reducing the attack roll penalty specifically. Powerful Build, on the other hand, removes penalties in general (of which increased handedness would certainly be a penalty of wielding a too-large weapon). And tossing out rules at will goes without saying; but this is a discussion of how it works as-written for a default state.
I'm pretty sure "penalties in general" is too liberal an interpretation. There is something actually referred to as a penalty by game terminology involved (the -2 to hit). If handedness isn't specifically called out in Powerful Build, while it is in other things like Monkey Grip or Wield Oversized Weapon (feats from the same 3.5 era and the makers of Powerful Build) or Lighten Weapon (here in Pathfinder era), then I'm inclined to think "without penalty" was applying to just that: the penalty.
In the end, there are still plenty of ways to wield ridiculously gigantic weapons with similarly gigantic base damage dice. Powerful Build just isn't the best one- there are tons of other things from 3.5 you can use (like an Alchemical Platinum Fullblade).
the ting i read is too large for her size, which to me means something she would normally not be able to wield, like a large 2 handed weapon or in the case of the half-giant a huge 2 handed weapon.
...
To me the wording on titan mauler means you can use a large 2 handed weapon
wintersrage, the reason that we're saying that doesn't work is because of the part I'm going to highlight. It's basically the last paragraph.
Weapon Size: Every weapon has a size category. This designation indicates the size of the creature for which the weapon was designed.
A weapon's size category isn't the same as its size as an object. Instead, a weapon's size category is keyed to the size of the intended wielder. In general, a light weapon is an object two size categories smaller than the wielder, a one-handed weapon is an object one size category smaller than the wielder, and a two-handed weapon is an object of the same size category as the wielder.
Inappropriately Sized Weapons: A creature can't make optimum use of a weapon that isn't properly sized for it. A cumulative –2 penalty applies on attack rolls for each size category of difference between the size of its intended wielder and the size of its actual wielder. If the creature isn't proficient with the weapon, a –4 nonproficiency penalty also applies.
The measure of how much effort it takes to use a weapon (whether the weapon is designated as a light, one-handed, or two-handed weapon for a particular wielder) is altered by one step for each size category of difference between the wielder's size and the size of the creature for which the weapon was designed. For example, a Small creature would wield a Medium one-handed weapon as a two-handed weapon. If a weapon's designation would be changed to something other than light, one-handed, or two-handed by this alteration, the creature can't wield the weapon at all.
Not only do you take an attack penalty, you need more hands every time the size category gets bigger. Lighten Weapon takes care of that for one increase. Massive Weapons doesn't do it at all, and I don't think Powerful Build does either, but others disagree.
Powerful Build, in 3.5, was F.A.Q.'d to clarify that the increase in Handedness is a form of Penalty.
That said the wording, if they were actually going off of 3.5's, should have been this allows the Half-Giant to wield weapons as if they were one size larger.
also this is straight from the Faq
The massive weapon class feature allows her to use oversized weapons with decreased penalty, but does not allow her to use two-handed weapons of that size in one hand.
If I'm reading this right, then the titan mauler class could allow a normal medium sized character use a large greatsword in 2 hands but not 1 hand.
The link to the Faq is here http://paizo.com/paizo/faq/v5748nruor1g1#v5748eaic9okv
You're not reading that right.
It is essentially telling you the exact opposite. It is about Jotungrip needing weapons to be sized correctly for the character, and then adding what we've been saying- Massive Weapons doesn't change the number of hands you need to wield a weapon.
The Archetype designer has stated they changed it from what he wrote.
Powerful Build, in 3.5, was F.A.Q.'d to clarify that the increase in Handedness is a form of Penalty.
That said the wording, if they were actually going off of 3.5's, should have been this allows the Half-Giant to wield weapons as if they were one size larger.
Looking at the 3.5 FAQ from Wizards, it does do that. Though it also states that effects like Powerful Build and Monkey Grip never stack.
also if the class could only ever get rid of -4 for Inappropriately Sized then whats the point of having it reduce the penalty by -6 over the class unless you could use a larger then normally allowed weapon. It just wouldn't make sense to make a variant class in a book that came out after the core book that, that gets ride of -6 penalty when the rules in the core book only allow for -4, unless the class can brake the rules because of the class.
Remember there is always an exception, the general rules and then the specifics of classes.
I'm not really trying to argue here, this is fun for me.
Anyway, the reason Massive Weapons reduces more than just -2 for inappropriately sized weapons is because you can wield Huge weapons- they just have to be the smaller categories of weapons (Light weapons, like daggers). Every difference between your actual size and the size the weapon was made for is another -2, as well as pushing the weapon category into needing more hands.
That is what is really limiting what weapons you can wield- it isn't the penalties to attack. You could just take it- Two Weapon fighters do that all the time. If the weapon needs more hands than you have to wield, that keeps you from using the weapon at all, and that is what you need special abilities to fix.
Closest thing I could find. I actually have my own houserule on them.
It was Errata sorry. They changed the Wording of Powerful Build.
Hence, the increasing Handedness.
EDIT: This is odd in my settings as I use Weapon Equivalency...
It was sort of like the Pistolero. They cut out certain lines to shorten it, but in doing so they change how the class works.
On the original post, no. Both Powerful Build and Lighten Weapon allow you to use a weapon one size category than you. Since your size is Medium(barring spells or powers tha change that of course, like enlarge person) you can use Large weapons only.
For the purpose of weilding a Large Falchion in one hand, this is true. But not a Huge one.
They would stack.
Lighten Weapon would be good for a Titan Mauler...
"This allows you to weild a weapon one size larger as if it were your own size, a two-handed weapon in one hand, or a one-handed weapon as light."
Please notice the bolded part of the sentence from Lighten Weapon. Half-Giants, no matter what Powerful Build does, are still medium sized humanoids. What's one size category bigger than Medium? Large. What does Lighten Weapon allow Medium creatures to do? Use Large two-handed weapons as if it were a Medium-sized weapon. What does powerful Build do? Allow Half-Giants to use Large Weapons.
Powerful Build doesn't change a Half-Giant's size for feats. Only Combat Manuvers/Defense, special attacks, and the ability to use weapons as if he were one size category larger. It doesn't affect he actual size, so he cannot use Huge weapons with Lighten Weapon.
EDIT: This is how I am reading it. This is how I would/will rule it in any of my games. If I have offended someone by doing so... well, that was not my intent.
The crunch part states you are lowering the amount of Effort needed.
And he is treated in relation to weapons as if he was 1 size larger.
I guess it depends on the Precedence of Effects.
So it is whether Racial Effects go before Feat Effects or not?
Well, either the creators of Advanced Feats(a wonderful series of products) or Jeremey from Dreamscarred Press would do the trick. A Paizo employee(which I guess is what you wanted, wintersage, as a GM from Pathfinder could be anyone on these boards. Myself for example) wouldn't be much help on a feat/race combo they had no hand in.
I would also like to point out, again it seems, that it is not a Half-Giant's size that allows them to wield Large weapons, but a racial ability.