The biohacker Immunology and Toxicology inhibitors (-2 to Fort saves and Sickened condition, respectively) have added two reliable debuffs for trying to make poisons viable. A studious biohacker can combine them both with Spark of Ingenuity, or two biohackers can double team. Combined with demoralize (which is increasingly easy with all the feat and item support) from a biohacker or a party member, it's not too hard to plan for inflicting a -6 to Fort saves on a tough enemy before loading him up with poison. (And consider the Malediction weapon fusion at higher levels to cast bestow curse as a reaction for another -4.)
And after you, possibly with support from the party, have heavily debuffed the enemies fort save, you don't have to be the only one shooting them with cheap poisons. The COM needler rifle and the COM/Armory injection pistols do very respectable damage in their categories, making it entirely reasonable for a soldier or operative to be attacking 3-4 times to support dumping a lot of poisons saves on a debuffed foe.
Does this make poisons practical? Yes to kind of maybe?
Injury Poisons
The following are ranked by cost. The first three come from COM, so you know they were thinking about this. We're looking for cheap, decent DC, preferably 2 cures for save, and preferably constitution track.
Amblaree, Level 2, 175cr
Type poison (injury); Save Fortitude DC 13
Track Wisdom (special); Frequency 1/round for 3 rounds
Effect Progression track is Weakened—Impaired—Blinded; no end state. When at the blinded stage, the victim gains the blinded condition.
Cure 1 save
Turbocurarine, Level 3, 260cr
Type poison (injury); Save Fortitude DC 14
Track Dexterity (special); Frequency 1/round for 4 rounds
Effect Progression track is Sluggish—Stiffened—Staggered—Immobile; no end state. Immobile victims can continue to attempt a saving throw each round as a full-round action to revert to stiffened.
Cure 1 save
Biocide, Level 4, 340cr
Type poison (injury); Save Fortitude DC 11
Track Constitution; Frequency 1/round for 4 rounds
Effect Select one living creature subtype when crafting biocide.
Creatures of that subtype take a –4 penalty to saving throws against the poison, and the frequency is extended for 2 rounds.
Cure 2 saves
Mindhaze, Level 7, 1000cr
Type poison (injury); Save Fortitude DC 17
Track Wisdom; Frequency 1/round for 4 rounds
Effect Upon reaching the weakened state, the victim can’t use telepathy or limited telepathy for 1d4 hours. Subsequent failed saving throws don’t extend
this duration.
Cure 1 save
Blue Whinnis, Level 8, 1400cr
Type poison (injury); Save Fortitude DC 14
Track Constitution (special); Frequency 1/round for 2 rounds
Effect progression track is Healthy—Weakened—Unconscious;
no end state.
Cure 1 save
Circuit Melter, Level 12, 8000cr
Type poison (injury); Save Fortitude DC 19
Track Strength; Frequency 1/round for 6 rounds
Effect This acidic poison is specifically formulated to also be effective against constructs.
Cure 2 consecutive saves
Docilant, Level 15, 20250cr
Type poison (injury); Save Fortitude DC 21
Track Charisma; Frequency 1/round for 6 rounds
Effect At the impaired state, the penalties from the weakened state become permanent until the victim benefits from a restoration spell.
Cure 2 consecutive saves
Strychnine, Level 18, 188000cr
Type poison (injury); Save Fortitude DC 20
Track Dexterity (special); Frequency 1/round for 4 rounds
Effect Progression track is Healthy—Stiffened—Immobile—Dead.
Cure 2 consecutive saves
Deathblade, Level 20, 132500cr
Type poison (injury); Save Fortitude DC 20
Track Constitution; Frequency 1/round for 6 rounds
Cure 2 consecutive saves
Biocide is the standout, provided you match it to the right subtype. Not too difficult in some scenarios (e.g. drow on Apostae, laushunta in a Castrovelan city), but Turbocurarine is an acceptable general purpose poison if you're planning to hit them several times and force them down the track even if they only ever fail one consecutive save.
Monster Comparisons
Let's see the odds of some monsters vs these low level poisons.
CR7 Aeon Guard Specialist, Fort +9
What's more natural than human opponents when you're up against the Azlanti Empire? Load up on that biocide. Debuff this fellow with shaken/sicken/-2 Fort and he's got an effective +3 against an effective DC 15, for a 55% chance to fail. Two or three hits and he's very likely to be really hurting, and this is well within the means of a lower level party.
CR 10 Void Hag, Fort +9
She's down to a +3 if you land all the debuffs, a 50% chance to fail against Turbocurarine, even a 35% chance against mismatched biocide. RIP, hag lady, if you focus fire her with a couple of characters.
CR 10 Stridermander Tyrant, Fort +12 (+2 vs poison).
It has the skittermander subtype, so you can craft a custom biocide, although it's not likely you would, certainly not in bulk. And it's got a decent Fort plus a specific poison resistance. But if you stack sicken/shaken/-2 fort on it you bring its save down to +8 vs poison, or a 25% chance to fail against Turbocurarine. The first stage of dex poison is a nasty debuff, so it's potentially still worth trying it at this cost and level. At least you get an extra 4 points of damage per hit.
CR 18 Contemplative Mentor, Fort +15
A full -6 debuff gets you only a 20% chance of turbocuraire succeeding on each hit, but at this level the cost is negligible so you should can be firing it indiscriminately at anything that isn't a high Fort bruiser. I include this one because its mental defenses are insanely high, showing that Starfinder is maturing to give save targeting abilities worth using to non-spellcasters. A biohacker build who focuses on fort save abilities (poisons, tranq dart theorem) and fort debuffs can pull some stuff off with preparation and a little luck against the right foes.
Final Notes
Get the Potency weapon fusion on your injection weapons for a +1 DC to those poisons.
Get the Conserving weapon fusion to save both your biohacks and your expensive poisons on a miss. Makes full attacking much less nerve wracking.
If your biohacker or an ally is a reliable demoralizer, consider skipping the sicken inhibitor from Toxicology and just investing in a cruel fusion, but that's starting to be a lot of weapon fusions and introduces another potential failure point and duration issue to screw up your debuff chain.
Don't forget you can administer a poison and a biohack at the same time, you don't have to wait, although depending on how much poison you can afford and how your GM handles order of operations on debuffs and saves you may want to.
The high level poisons are mostly awful for their cost that doesn't justify the boost to DC and the 2 save cures, but I do wonder if the Circuit Melter is potentially worth stocking a couple of doses for use against tough constructs. Definitely have a conserving fusion, though.
Looking beyond injury poisons, I just realized how horrifying/useful the Charisma track poisons can be for interrogation or making slaves.
Charisma Poison Track
Healthy—Weakened—Impaired—Pliable—Catatonic—DeadPliable
The victim has little sense of self and goes along with nearly any order or suggestion. Creatures attempting Bluff, Diplomacy, or Intimidate checks against her automatically succeed, though Diplomacy checks to improve her attitude still have the normal DC.
So if you're pliable you do pretty much anything you're told by anyone. "Sit in that corner until I tell you otherwise." "Cast X spell to do Y thing. Ok, go back to your corner." "I'm conducting an audit for Azlanti high command. Tell me all about your fleet's plans and what weaknesses you see that the enemy could exploit." "Log on to your mainframe and transfer these files to my comlink."
How to reliably hold them at pliable before they go to catatonic, you ask? Two ways.
GREEN LOTUS EXTRACT, Level 8, 1500cr
Type poison (contact); Save Fortitude DC 18
Track Charisma (special); Onset 1 minute; Frequency 1/round for 6 rounds
Effect progression track is Healthy—Weakened—Impaired—Pliable—Pliable. The second pliable functions as an end state.
Cure 1 save
Four failed saves, which will likely require more than one application, even with heavy debuffing, makes someone permanently a pliant zombie. You can't heal naturally from an end state, and only wish/miracle type stuff can fix it. Scary as hell, I imagine overly confident high level spell casters with low fortitude saves having their volition burned out by a prepared biohacker and turned into their lair-based spell slaves.
But there's also a way to achieve temporary pliability for field interrogations, security system bypassing, etc.
Breakthrough
You can use the following ability when you achieve the breakthrough for this field of study.
Suppress Poison (Ex): As a standard action, you can create and deliver a formula to a living creature that holds the course of a toxin in check. When injected, the formula allows the target to ignore the effects of the highest stage (not including the poison’s end state) of a single poison affecting that creature for 1 minute. The poison doesn’t progress normally during that time, but this time doesn’t count toward the poison’s duration.
If you are at least 7th level, the target ignores the effects of the highest stage of a single poison for 10 minutes. If you are at least 13th level, the target ignores the effects of all stages of a single poison for 1 hour.
Use any Charisma track poison and once they hit Catatonic hit them with the initial or 7th level version of this breakthrough. They stop making saves, so no risk of death, and revert one stage to pliable for 1 or 10 minutes. Have them answer your questions, log on to a computer that they have access to, or anything else a brainwashed p-zombie would do. After that one or ten minutes, they go catatonic again and potentially die. Feel free to treat the poison if you want them to stop at catatonic for a day and possibly reuse them with another wake up.
The only other two Charisma track poisons I'm aware of (not in APs or AAs) are actually higher level than Green Lotus Extract.
UNGOL DUST, level 9, 12500 cr
Type poison (inhaled); Save Fortitude DC 15
Track Charisma; Frequency 1/round for 4 rounds
Effect At the impaired state, the penalties from the weakened state become permanent until the victim benefits from a restoration spell (see page 374).
Cure 1 save
DOCILANT, level 15, 20250cr
Type poison (injury); Save Fortitude DC 21
Track Charisma; Frequency 1/round for 6 rounds
Effect At the impaired state, the penalties from the weakened state become permanent until the victim benefits from a restoration spell.
Cure 2 consecutive saves