Grappling:
Ok...again I suddenly don't understand a rule I've been using for ages. Duh.
Now, upon re-reading everything, this is how I see it:You need IUS or the monk class feature to deal lethal damage in a grapple. Natural weapons count like normal weapons - you use them with attack rolls at -4. And in any case, the base warforged slam attack deals 1d4, improved to 1d8 when huge, 2d6 when gargantuan.
You can't use them in opposed grapple checks. And base unarmed damage.... blows. It's 1d3 non-lethal base for a medium creature, which means a gargantuan creature deals about 1d8. Which still blows.
So let's just say the Adamantine Body feat changes this: You get a 1d6 slam, deal 1d6 unarmed (as medium) and lethal, but still provoke against armed opponents. Because it doesn't make sense that a gentle embrace of steel doesn't deal lethal damage.
And then there's armour spikes. Thistle has been using them in the way that they simply add to the unarmed base damage. So it's 3d6 bludgeoning, 3d6 piercing, +Str. I'm not quite sure that's what's intended, but the complete lack of a proper explanation, and the funny wording the armour section of the SRD seems to suggest he's right.
Now I've checked again, actually you can't crit on an opposed check, so you can't crit on a grapple.
So just roll damage for the second grapple check.
