The Tavern

Poison is a wonderful mechanic that doesn't live to its full potential. It is deadly in early dungeon, and it stops being relevant once player finds source of poison resistance. After that it essentially turns into cantrip. This is a major source of power creep - if spiders were able to actually poison the player, spark wasps wouldn't be necessary. Having rPois is a no-brainer and it heavily cuts challenges from middle and late game. Here are some examples of relatively high-HD things being less because of having poisonous flavor:

Thing	Can be treated as
Redback	Wolf, but it can't see invisible.
Green death	Swooper, but without swooping.
Water mocassin	Centaur, but without ranged attack.
Snake pit	Orcish mines with less shops.
Swamp drake	Crocodile, but it confuses other monsters.
Golden dragon	Iron troll, but it can't open doors.

Also, I challenge anyone to play a game with no poison resistance from items and not naturally resistant species (not Mu, Na, Gh, Vp or DD). It isn't MuMo, but it's still a fun experience.

I don't understand why you call it fun experience. Losing 50% HP without monsters in view is not fun, retreating to stairs, using them and then pressing 5 multiple times is not fun. Or do you hope the removal will trigger changes to poison mechanic?

I would be in favour of reducing poison duration dramatically, 50 aut max, and in turn increasing the damage per aut, but not the max damage.

In order to make poison more like the early game, wouldn't you also need to prevent !curing from curing poison? Maybe also increase the amount of poison given by attacks by 50% or so.

Maybe rPois should just increase duration without changing total damage

Removing rPois sounds reasonable to me, but I'm scratching my head at the suggestion that poison is a "wonderful mechanic." Poison, in the sense of a status effect that does damage over time, is remarkably tedious both as a monster effect and as a player effect. Damage over time is easily countered by one of the most common items in the game when it's dangerous and annoying to deal with outside of combat when it's not.

DCSS is unfortunately heavily committed to the poison concept with a lot of content based around a poison theme and some key monsters, notably adders, having poisonous attacks. If poison is going to be a thing, the game already has a better model for it: hornet poison. I suggest phasing out the damage over time type poison in favor of hornet poison, with whatever adjustments are thought necessary for balance.

I'm pretty sure I've already done this like 40 times without noticing

I honestly can't even tell the difference between rPois and no rPois in spider, and barely notice it in Snake

Maybe if rPois gave you tarantulla immunity(which would also make them not really really obnoxious to mummies)

While we're at it, can fewer lategame monsters be poison immune please?

Well, a lot fewer are immune now than used to be after the demon change.

Change poison to deal percentile-based damage, like torment. The specific percentage can be lower. Or not, whatever. The poison status would have a few turns of delay after you get afflicted before you get the damage, and then it either clears up or you get another random delay before you get more damage. Curing during the delay prevents the damage, and if you rest in place with no monsters on-screen you likewise clear the status and prevent further damage. The percentage of damage can be high enough to be legitimately threatening during combat, while being less annoying once combat has concluded. These are both better than the status quo, where poison almost never matters in combat past the very early game but is annoying to get rid of since it causes constant interruptions.

Something like 25% of your current health is probably a good number for a poison tick. If you have rPois, either the damage can be lowered somewhat, or you can get a longer delay between ticks of damage, or you can have an increased chance of clearing the status after a tick of damage.

Two suggestions for poison effect on player:
1) Prevent regeneration while poison is active
2) Prevent poison over time damage being lethal

I really have to question the existence of damage over time effects at all.
When a monster is suffering from a damage-over-time effect, the player is encouraged to kite and wait for the damage-over-time effect to kill it, instead of engaging it. This is immediately apparent on any character that uses poisoned needles, sting, poisonous vapours, a venom weapon, sticky flame, and so on. Given that "luring" is reviled, kiting a monster waiting for poison to sloooooooowly kill it is surely even worse!
When a player is suffering from a damage-over-time effect, it's not likely to change their actions in combat, with the exception of spending a turn to cure it (which is no more interesting than any other "lose a turn" effect). You can say "well, it encourages them to end the fight with enough HP to survive the DoT" but you're already quite obviously encouraged to end every fight with as much HP as possible, DoT or no DoT; the DoT just makes it harder to count how much "real" HP you have. If you just did the DoT damage up front then it'd be both strictly more dangerous and much less annoying.
Similarly all these regeneration-stopping/reducing things like sickness and that one mutation are effectively DoTs, since taking away your healing over time is the same as doing damage over time; there's no difference between disabling your 1 HP/turn regeneration and dealing 1 damage per turn.
And while DCSS may be overly invested in the flavour of poison, there are very few monsters that rely on the Pois effect to work. Worker ants, snakes, killer bees, wolf spiders, spiny frogs, etc. would work perfectly fine with no poison and slightly higher base damage. Naga poison spit, gold dragon poison breath, etc. do so little that removing them from monsters would probably be a buff to those monsters. Redbacks and swamp dragons are specifically invested in poison, but they're also pathetic jokes of monsters because you can just quaff curing or not stand in the poison clouds.
As for player-available poison, there's a magic school that nobody likes, miasma clouds which could just do higher immediate damage, a weapon brand that people only use because it's OP in the early game, poisoned needles that most players don't even bother carrying anymore, naga poison spit which could easily be replaced by another breath weapon if nagas must have a breath weapon, and stingers, which don't need to have poison.

Poison being something which cuts HP by a percentage could be interesting. Being its own school with that idea wouldn't be justified, of course, but what else is new.

I think DoT is a legitimate mechanic. Doing damage over time to an orc priest (or summoner, or a monster with lightning bolt, say) is more dangerous than doing damage up front. Therefore, it is legitimate for freezing cloud to do more damage over time than a direct damage spell would, because the player is risking more by keeping the monster alive longer.

Poison might work better if it was based on the freezing cloud model: you have to stay in a certain square for the poison to keep working. I don't like the poisoned status model because it leads to lots of backward moving while you wait for the poison to act. Sticky flame has the same issue, mitigated a fair bit because you need to be in melee range to apply it. Summons have the same problem, but it would require a lot more to fix them.

Poison and freezing cloud could be differentiated by making the damage linear (or some other function) in the number of stacks of poison instead of roughly fixed damage per turn, as in the case of freezing cloud.

The Snake Pit is far more deadly than the Orcish Mines even with complete poison immunity.

The rest of these examples are probably also exaggerated.

Edit: In terms of straight up monster strength. I realize you can run from a lot of stuff in Snakes.

Characters with rPois can, and do, still get poisoned, just at a lower rate. In practice, it just means that the number of poisonous enemies required to bring down a character increases. Poison immunity is a different story, but that's not available to most player characters.

I don't think poison needs buffing or poison resistance needs nerfing. Poison is highly capable of being dangerous without poison resistance, and still manages to play a role in combat even with poison resistance. True, the threat of poison tapers off as the game goes on, but that seems like a deliberate design choice. Hence why the poison-themed branches are encountered in the first half of the game; and none are found in the late game.