Shitty attempt at short version: Antags and captain+sec can both use it. It starts as hard-to-detect gas, breathing it or taking contaminated meds/food/drink doses you with reagent, cumulative effects slowly make you less effective at combat & lets security micro-stun you by yelling at you to stop. If crew catches on and communicates it's fairly easy to counter, if not it gives those in the know a significant edge.
How is Pax deployed?
Pax starts as a gas that can be released into the air and will slowly self-purge. There's two canisters of it in the sec office by Atmos, possibly one canister in Armory or even Science, and traitor uplinks lets you cheaply buy tanks of Pax that look like regular emergency oxygen tanks.
Analyzers will detect Pax in the air (possibly as "unrecognized particulates" instead of "Pax"), but air alarms won't trigger alerts or attempt to filter it unless you've changed their settings. At low concentrations, the gas is otherwise undetectable- players get zero direct notification when they're breathing it. Anyone without clean internals or a gas mask will have the Pax reagent gradually build up in their system over time (it metabolizes very slowly.)
However, an alternate tactic is to release Pax in high concentrations. The downside is that the gas becomes visible as white flecks, same as how there are visual effects for high levels of gases like plasma- the larger the area affected, the longer it takes to disperse & the greater chance someone will see it happening. But the upside is a strong one: Pax contamination in any tiles with visible particles. This creates new hidden vectors for getting the reagent form of pax into people's bodies- food, drinks, patches and pills that have been contaminated, either from direct exposure or thanks to pax-contaminated objects like tables, gloves, sinks, etc.
Implementation details:
The gist of the concept is that Pax makes you more compliant and suggestible, especially in response to auditory stimuli. The symptoms are generally subtle and accumulate based on how much of the pax reagent is in your system.
LOW DOSAGE (breathed air with low amounts of pax gas for half a minute, used a pax-contaminated brute patch):
-Slight increase in duration of slips and stuns, starts at 10% but increases with higher dosage.
-Small chance (starts at 10%) to freeze up (stop moving and take no actions for half a second) if you hear a statement containing words like "stop," "freeze," "hold", "halt", or your character's (real) first/last name. 5-second cooldown before you can be made to freeze up again. (may not work over comms?)
--Chance can be boosted by 20% if statement is loud (i.e. through a megaphone), or is said with exclamation points.
--Chance is boosted by 40% for ALL compli-o-nator messages and beepsky alerts. NanoTrasen's been fine-tuning their speakers for maximum effect.
MEDIUM DOSAGE (inhaling low pax amounts for 5 minutes straight, ate a giant pax-contaminated burger)
-Base chance to "freeze up" increases to as much as 50%.
--When you do freeze up, 50% chance to let go of anything you're pulling & also change intent to helpful.
-Attacks & disarm actions have 10% chance to miss (or maybe give you message saying you hesitate?).
-Suggestion-induced hallucinations? This one's probably the most ambitious thought, will leave it for another post.
HIGH DOSAGE (inhaling low pax amounts for 15 minutes straight, hit by a couple syringes holding 15u of distilled pax reagent, survived long battle where you repeatedly healed yourself with pills & patches while wearing contaminated gloves.).
-Attacks & disarm actions also get like 10% chance you'll target yourself AND a 10% chance that you'll drop any held item instead, for a total of 30% chance for attack to fail
-Chance that hearing statements with words like "kill", "lynch", "murder" or "attack" will change intent to aggressive.
How do you detect Pax?
Both the gas and reagent show up to analyzers just fine. Pax contamination of tables, sinks and hydroponic trays won't show directly on reagent scanners but can be confirmed through simple tests (confirm the orange has no pax, put it on table, check again.) Forensic scanners will detect all forms of pax contamination and even mention pax particles found on fingerprints and glove fibers. It could even hint towards how precisely a consumable was dosed- "totally covered" in pax particles if it was tainted by gas or sink, else "the underside is totally covered" if it was tainted by table or floor, else nothing (because any pax reagent was either injected in there by syringe or was present when the item was created).
You know it's Pax. How do you counter it?
Things like charcoal that purge chems don't work great against Pax (Either A: because the reagent somehow ignores the purgatives that work on every other chem, or B: because purging Pax reagent only stops the symptoms from increasing further, rather than undoing them.) The antidote to Pax is Synaptizine, which chem can make and botany can supply by growing ambrosia deus. Synaptizine will purge Pax from your system & quickly cure the symptoms. Not only that, a mixture with at least 1u of synaptizine can be sprayed on any tile to purge the pax contamination from all exposed objects.
Beyond that, there are lots of brute-force methods to mitigate the issues. Don a gas mask or use internals with a confirmed-pure gas mixture. Wash your hands/gloves in sinks if you can confirm they're clean. Stash clean gloves in your backpack or box and take them out only when eating or applying meds. Dismantle tables +floors and replace them. Grind things down and use chem-masters to filter the chems out. If your nefarious saboteurs/tyrannical authorities are abusing compli-o-nators, deafen yourself or don earmuffs.