I'm a little new to the game. How is CR calculated? I couldn't find it on the SRD.
Yeah, PC's are generally referred to as being the same CR as their class level (this is different from npc's, due to players typically having better gear/party synergies). To adjust this, add either the abilities discussed on the first page (I'll put rulings like that into the OP for reference soon) or templates, found
here. The CR+1 templates are especially nice, since you're allowed 14 class levels but need 1 extra CR.
On another note since someone mentioned it earlier and I don't think I got around to answering it, I'd count the standard drow as a CR+1 race. If you take out the spell resistance or the spell like abilities, then they're CR+0. (Regular races are between 8-12 Race Points). Similarly, Kobolds and similarly weak races are CR-1.
Internal alchemy. Like your insides can be used as an alchemical workstation with the final material excreted through fangs.
Assuming you're asking about doing that, then I'll allow you to count it as a sort-of archetype- You can forsake poison resistance, swift alchemy, and swift poisoning to substitute for internal alchemy:
Internal Alchemy: (gained at level 2)
As you prepare your formulae for the day, you may use your inside as an alchemical workstation. You may prepare a number of formulae equal to half your Constitution score in this manner. If the formula is an effect that is beneficial to you, you may absorb its effects at any time within the next 24 hours as a standard action (down to a move action at level 6 and a swift action at level 18). If the effects are harmful, you may excrete them through your fangs to produce either a magical bite or a magical spit. A bite functions as a bite attack at your base attack bonus-5 +1/2 your strength and counts as a secondary natural weapon(1d6 damage for a medium sized creature). Spittle counts as a ranged touch attack with a range increment of 10' (5 increments max). Either of these attacks are a standard action. You may also use your bombs in a similar manner, but storing more bombs in your gut takes 1 minute per bomb, and they count towards your limit of formulae stored internally.
At level 18, you may use your internals to create alchemical items as well, as described in the instant alchemy class ability, but secreted in the manner described here.
If you have the Infusion Discovery, you may also inject a formula into an ally as a bite, but you may forsake the damage to your ally if you so choose.