In pathfinder and 3.5 before it, poisons have traditionally been terrible for three reasons:
1. They are expensive
2. They are too slow to meaningfully affect NPCs that are going to die in 3 rounds anyway.
3. There is very little build support for poisons in the system, because poisons are evulz.
I was looking through the Archive of Nethys recently, and discovered that there are now a bunch of cheap poisons that apply status effects! So I made a neat little build that should be PFS legal. One thing to keep in mind is that poison is still poorly supported with feats and items. So you can't really build a poisoner the same way you can build, say, a fire sorcerer. So the build will be a fighting-person who also poisons, and will have some gaps that you can season to taste.
Agatha Blackhand, Neutral Female Human
Unchained Rogue (Poisoner) 4 / Alchemist (Eldritch Poisoner) 4
Strength 13
Dexterity 17 + 2
Constitution 12
Wisdom 12
Inteligence 12
Charisma 8
Traits: Poisonous Slayer, {open trait, but probably reactionary}
Rogue 1 - {open feat}, Poison Focus, Poison Use, Weapon finesse, Sneak attack +1d6
Rogue 2 - Lasting Poison, Evasion
Rogue 3 - Super weapon finesse, {open feat}, Sneak Attack +2d6, Master poisoner
Rogue 4 - Swift Poison, Debilitating injury, Uncanny dodge
Alchemist 1 - Arcanotoxin, Sneak attack + 3d6, {Any feat, retrained to vital strike at level 8}
Alchemist 2 - Concentrate poison
Alchemist 3 - {Any feat, retrained into Deep Toxin at level 8}
Alchemist 4 - Careful Injection, Sneak attack + 4d6
So now onto the exciting part, how this would play.
At level 1, You are basically just an UnRogue. Take your rapier and attack for 1d6+1 damage!
At level 2, we get our first poison efficiency. Now Agatha can make 4 attacks with one dose of poison. She will use Red Tears To add a DC 14 fortitude check on each attack she makes. And because of Poisonous Slayer, this gives her +1 to hit, all at the cost of 50 gp.
At level 3, we get the ability we've taken rogue levels for. Agatha can now convert poisons delivery mechanisms with a trivial Craft(Alchemy) check. In important fights, she will use Confabulation Powder, Either by throwing it to control the battlefield, or pre-applying it to her rapier. She will be making enemies staggered with a DC 17 fort save and she will get 4 attacks from this for only 80gp.
Oh and Agatha just got Dex to damage. Level 3 is a good level.
Levels 5 through 7 get us the alchemist's arcano toxin. Which does not accomplish much. But it counts as a poison for all of our abilities. We also get Concentrate poison which lets Agatha spend double a poison's price for +2 to the DC. Around this level, Agatha should be able to afford a +1 spell-storing weapon. The spell she will store is almost always going to be Pernicious Poison. Bonk some fool with your weapon and suddenly you get +4 DC to your poison. You can buy castings of pernicious poison in most settlements for only 60gp and a day's wait. Or buy a wand of it.
At level 8, (or level 9 if you don't want to spend 10 prestige retraining) you get your build capstone. And what a capstone it is. First we take some Chellish Deathapple; it's a poison that makes a creature unconscious for one minute with a base DC of 23! Unfortunately, the poison is ingested and has a 1 minute onset. That's ok though. Master poisoner lets us convert this little fiend into an injury poison, and Deep Toxin lets us bypass the onset time when we use vital strike.
At this point, Agatha has likely bought a dexterity belt, so with only 200 gp, She is forcing a save or die on 6 attacks with a DC of 22. But that's not all. When it's time finish off an important foe, Agatha can drink an extract of invisibility, activate her spell-stored pernicious poison, and trade off 4 dice of sneak attack for +8 total to the save DC. She can further spend an extra 200 gp for another +2 to the save DC.
Hows that DC 32 save or die effect looking. Oh and I guess she deals 2d6 + dex damage or something too…
I'm not sure what you do after level 9+. You could take more rogue levels to keep your sneak attack up. 4 more levels of alchemist will get you celestial poison which will let you put undead and demons to sleep and the ability to add extra strikes to your poison equal to your intelligence modifier. Another 6 levels of rogue will get you Deadly Cocktail, which will let you put two doses of your concentrated applesauce on your sword for another +2 DC.
Brewmaster would arguably increase the DC of your Chellish Deathapple even after you convert it into an injury poison.
You can take Power Attack and Powerful Poisoning to boost your DCs still further.
Anyway, so now that's how you poison things. This is also how you cry when you discover that you are going to be fighting robots for the next 8 levels :'(
Updates will be located at this google doc
Looks good, even if multiclassing rogue and alchemist makes me twitch (yes, I know vivisectionist isn't PFS-legal).