Poisoners require a hyper-developed sense of planning. You need to manage and plan
- your career path
- you gold reserves
- your currently brewed poisons and how long they will last
- your poison ingredients (I always carry knockout and neurological ingredients)
- if you plan to use mind control, what other props you plan on using (fillets, amulets, pills, weapons, non-weapons, blindfolds)
- and of course your weight & whatever other preps you want to use.
If your enemies can't bash you, they will probably recall as soon as any poison lands on them. If you are a pure poisoner, and you still can't apply inhaled on sleeping victims, knocking them out gives them time to formulate a plan, and killing them is that much harder. If your goal is to actually kill them, catching them when they are spamming (running along the road) is very useful, and of course fighting them in a no recall area.
I mastered pickpocket early, and I found it beneficial for people I planned on killing to clean them out of potions before I let them know I was there. If I didn't steal your potions (like Aalim in the Fortress) then I wasn't making an honest attempt at killing you.
I mastered improved hide and had covert quite high (90s, I think) and I still stepped out whenever I did anything with poisons. I was quite frustrated that I had spent the points on both to still have my hiding compromised whenever I wished to prepare for a fight.
Don't envenom all your weapons, for you need to be able to have a backup weapon if your target is immune. I liked to envenom one weapon with a regular attack (like tiny iron dagger), and apply neurological poison to that weapon and my offhand wrathing weapon. If I had time and money, I'd keep fear on a third weapon or in grenade form.
Grenade uses one pure ingredient; you cannot create a grenade from previously concocted poison, and you cannot apply poison to a grenade in an attempt to stack effects. You can launch grenades within combat, giving you TWO WHOLE poisoner skills! Launch seems to be pure dex; I don't recall ever getting hit by my own grenade (25 dex), but it seems like they are too easily evaded. It is very annoying when a sleeping character somehow evades your grenade, given the gold cost and lag associated with launching.
Playing an arial scout was a great route for a battle poisoner; during actual combat, critical hit offers something you can do within combat against poison resistant or immune characters, and it cut down on my weight because I didn't need to carry personal preps. The downside is that you can't pick on non-mages of the Fortress and Heralds, the people most susceptible to hiding classes, or Battle which is most susceptible to maladictions.
I love the path, but I hate farming gold, and I wouldn't play a poisoner with a stupid race.
A question I never bothered to figure out: how much does formaldehyde lengthen the shelf life of your poisons?