My game of choice is Exalted so I don't get to use them often, but when I do...
Immunity to Everything Technique has become something of a priority for my players.
Guys, I'm an alchemist. Assassins think they're master poisoners with their Use Poison ability, but an Alchemist does it at level 2. At level 2, we also have a +2 to saving throws against being poisoned, that scales until it becomes an immunity at level 10. At level 6 we use poison as a swift action, meaning I can move, hit with a poisoned weapon, and poison my weapon for the next strike in the same round. Craft Alchemy becomes fester with levels, to the point a lv 18 Alchemist will make a poison (or anything) with a full-round action. Plus there are the Sticky Poison Discovery that allow a poison you craft to remain on your blade a certain number of hits, making it less of a waste of money, and a few other Discovery that allows you to do things people wouldn't dream about.
Now a story... How about when we found a dying balor so desperate to be freed/saved that he'd promise ANYTHING without a second thought? He gave me a ludicrous amount of his venom, since it was litteraly oozing from his fangs. My character had a "Fumble Dagger", a dagger that deal only 1-2 damage thanks to my lousy Strenght, and I rolled Nat 1 3/4 of the time with it. I coated it with the venom, and to this day I call it the "One-Hit Kill Dagger" sonce it does 1d6 Con per round with a DC so high they're condemned the moment it hit.
Came to bite me back when a NPC decided to surrender and amend, but there was nothing we could do except watching her die and feel guilty. (Seriousy, Neutralize Poison is probably worse than the good ol' Fort Save!) About the same time, though, I got the Celestial Poison discrovery, which allows me to poison poison Undead and Evil Outsiders (AKA Demons), so my character vowed to utilise the Balor's gift only on those. (It was decided the venom wasn't supernatural, but rather a mundant substance created by his body, so it is indeed possible.)
Recently, I invented my own poison, harder to resist than the Balor's, that deals just as much damage, except that it lowers Dexterity instead of Constitution. It keeps the victim alive and conscious, so we don't have to watch them die despite their surrender anymore.
Story Time! Tell a story about Poisons (magical or otherwise!)
Allow me to introduce you to a wonderful thing called the biotox pouch. Originally a thing for Raxon, I have adapted it to 3.5. It's a graft. A small organ in your abdomen that requires fleshcrafting, and the bladder of a donor.
Basically, any poison you succeed in a fort check against is added to the sac, and you can release those poisons into your saliva and spit them at your enemies, onto your weapon, you name it. It is a supremely useful little organ. It costs 15k gold, and has a storage capacity of about a half cup, any excess poison must be purged.
Please note, if you fail the save for the poison, your body does not extract the poison to the sac, so being poisoned intentionally is a very bad idea.
So it's like having Dan Mc.Ninja's eyeballs in your salivary glands?
Yeah. There's also another goodie, that is similar, but for alcohol. See, the organ stores alcohol in a very pure, concentrated form. As a move action, you can fire a spray or a stream of it out. A nice binge and a candle basically means you get dragon fire, without the risks inherent in draconic grafts.
Raxon has one. You have not seen frightening until you have seen a scrawny little man down two 40 oz bottles of 98% alcohol in the span of an hour while watching cartoons and taking notes.
Seriously, this is the kind of behavior that his associates describe as "unsettling." When confronted, he asked if they had a light. He proceeded hold the lighter in front of his mouth and scorch the bulkheads. "Thanks for the light." He then pulls out a little recorder. "First tests of alcohol storage pouch seem to be successful, though the nozzle needs some calibration for optimal distance and spread."
You know, because rigorous testing, controlled lab environments, and ethics regarding test subjects are for the pitiable masses without access to biomancy and the ability to regrow a face.
Also, since he's kind of a dick, this is more or less a way to give the middle finger to pyromancers. "Sure, I can do that." And then he proceeds to whip out a case of beer and start chugging. "Hold your horses. Once I get enough of this stuff in me, I'll be right on your level."
Why yes, he does have immunity to most nonmagical poisons, and yes, alcohol counts. Fun, right?
So we're playing DnD5e right. and one of my players really wants to play an assassin, he was overjoyed that FINALLY you didn't have a crazy prerequisite like killing a loved one or something similar to be an assassin. and then he spotted the poison makers kit that assassins can use, once again overjoyed! Then he went on to look at poison rules and was slapped in the face. poison gives the smallest damage boost if anything as well as is really difficult to do. and nothing he could do to build his character would let him make it in the right way to make him a good poison user. He wouldn't let his inner optimizer to do it, (which is his own fault) and then he hanged his head low and made a paladin. He still cries on about it.
While Assassins can be pretty good in the right circumstances with their autocrits in the surprise round, I definitely prefer the Thief. Having Use Object as a bonus action (which the Thief gets at 3rd level), and then taking the Healer feat means that you can bounce around combat getting your party members back up to 1hp as a bonus action with healers kits, then get to attack with sneak attack damage because your party member isn't incapacitated anymore. Add in the Mobile feat and you can then run away again without provoking an attack of opportunity.
Admittedly it can be more fun sometimes to be an orc champion with a greataxe, but there's something to be said for doing a bucketload of sneak attack damage most rounds along with healing your party members with bonus actions.
I usually stick to the pony comic for stories like this but... short and simple one.
First game of a new Campaign, new system... and bar a test session, my first time GMing. Mutants and Masterminds, with Marvel. It was simple enough, the Serpent Society had robbed a museum and everyone was gathering together for the first time and chasing them down. Then I declared one of them was using a poison attack. Ends up there's one power that gives immunity to suffocation... and all poisons. We've agreed since that unless you can justify it, no Life Support
Hmm, so is it a disease or poison?
If disease, shoulda been a paladin :P
Oh, wow, we haven't actually seen her go motormouth in a while, have we? I kinda even forgot she did that.
I for one hate fighting swarms. That being said, I once talked my DM into allowing me to use Craft: Alchemy to create rat poison to deal with a large infestation of rats. It helped that the party's wizard was Chem major and told the DM that making rat poison isn't all that hard. At any rate, any time our group passes through a town I now sell my services as an exterminator.