Worship norg. Take the Obedience boons that let you choose your rewards. Choose the ability that adds +2 to the DC.
Be: An 8th level Witch +. Preferably Tengu, for the Claw Claw Bite.
Add 2-3 more natural weapons via your method of choice.
2 Levels of Alchemist - so you don't poison yourself.
Spell Storing on a weapon (or ring, or quicken): Pernicious Poison. UMD a scroll.
Buy a Bottle of Misfortune. (500gp) Bottle up a few Evil Eye.
So, by some miracle (or you use another character to actually do the attack routine:
Evil Eye. -4 for Int rounds, or 1 round on a save.
Pernicious Poison: No save. -4 to poison save.
Norg: +2 DC.
Go with something cheap. Vampire Kiss. Crafted yourself 25 gp per does. 1d2 Con damage.
6 total attacks, 1 Evil Eye, 5 Vampire Kiss. So 5 DC 17 checks at -8.
Lets go ahead and get excessive:
A. Fleshwarped Scorpion tail, enhanced with spell storing (pernicious poison). Graft it on. You can now deliver touch attacks, and poison.
B. Wayan Spell hunter. Magical lineage. Quickened Accelerated poison.
12 checks. Plus two d4 FWST DC modified by your Orc witchdoctor con. Each failure increasing the DC.. and the duration.....
I'm not suggesting this is particularly playworthy. But.....
Not usually a legal choice since you have to be a half-orc or orc to take Scarred Witch Doctor normally. But if your GM allows you, that's fine. I feel racial archetypes are harder to justify over other racial specific stuff though so good luck.
Ground rules: Use Unchained Poisons. Firstly, it deals damage even when they succeed against the DC (our DC is so high that this is impossible short of a 20, but whatever), and multiple applications actually accelerate the creature along poison track rather than increase the DC. This means that, with Haste and a full attack, we could get a creature down to near death in a single round regardless of their hit points. This is the fundamentals of the build. Death by papercuts and deadly neurotoxin. We only need to do enough hitpoint damage to inflict the poison, so I hope you can roll high enough to bypass DR. Hence Mutagen and Sneak Attack. And why this build uses Slashing Grace (but feel free not to if you so please and if you prefer Power Attack).
We're playing an Alchemist. Obviously.
Start off Human, get Racial Heritage (Nagaji). Use this to take your new nagaji favoured class bonus every level.
Take Potent Concoction. We'll need to worship Ghlaunder but frankly poisoners are not nice people anyway. Choose two poisons you wish to use frequently. I took Giant Wasp Poison and Purple Worm Poison for cost effectiveness and high DC.
Get a Kasatha Spine Sword. Get proficiency (via EWP). Make it a Virulent weapon. Take note, normally a ratfolk specific special ability, but honestly just go find a ratfolk artificer to make it for you and you should be fine.
I chose to go Vivisectionist and Toxicant to give use some stopping power early on. Vivisectionist is the only important one of the two, since we need it later for other options (Pernicious Stab), but Toxicant allows us to make the most of our poison options by giving us a potent free poison tool. The debuffs also allow our poison to more easily land if we can get it off.
We need to take all the poison discoveries. Just...just take them. Get mutagen as well. It's mutagen after all.
I would also take Master Alchemist to accelerate poison making.
Lastly, abuse Alchemical Allocation like the cheap powergamer you are.
So it's a tengu with an orc archtype?
Sorry that was a throwaway comment, not really serious.
The essential idea to make poison possible is that you have to
a). Get a large number of doses delivered simultaneously.
b). Get the save DC's up.
Natural weapons, (or an animal companion, or arrows or shuriken) accomplish the former.
Pernicious poison and Bottled Witch hex accomplish the latter.
But I do like the idea that you can graft an enchanted flesh warped scorpion tail onto your animal companion.
Be an Eldritch Poisoner Alchemist and take 2 levels of Daggermark Poisoner (AKA Guild Poisoner) to get a multiple use Pernicious Poison spell-like ability. Pernicious Poison doesn't give a save, so you don't even need to progress further in the Prestige Class to up the DC; just don't use it on something that has Spell Resistance.
For Feats, get Master Alchemist for better crafting. Poison Focus, Pernicious Stab and/or Treacherous Toxin, and possibly Daggermark Lore (AKA Dread Poisoner's Lore) for better DCs. Powerful Poisoning if you want to use Power Attack for some reason.
Bonus points if your friend is playing a Witch for that sweet Evil Eye Hex.
EDIT: HOLY CRAP! I just realized you could probably take Daggermark/Dread Poisoner's Lore for the Eldritch Poisoner's Arcanotoxin! It has a stat block like any other poison, so it's not just an ability.