A Daoist mystic, actually. Which is irrelevant. The point still stands that RW "shamans" used more than herbs in creating their medicines and "magical" concoctions. Gunpowder was discovered by accident from a Daoist mystic trying to create a medicine. Therefore, someone creating experinental medicines can accidentally discover gunpowder regardless of being a shaman, a daoshi, or a Nickleback fan.Sure, but he was a researcher/chemist, not a shaman. Probably working directly for the Chinese Imperial Household.
Outright theft or Fiat Ka-boom are going to be seen as arbitrary, so many of the recommendations here aren't feasible or in any way linked to gunpowder... they are just linked to explosive weapons, which any wizard or cleric potentially qualifies as.
Playing on the particular weaknesses of gunpowder is fine. Making everyone and their monstrous mother suddenly aware of them is not.
1) there are some with fire res/immunity. Over the overall numbers, very few. Tons of hp = use more gunpowder or set up a collapse.
2) Who said I was saying it was common?!?! The OP said the PC's are using it, potentially a lot of it. He said nothing about EVERYONE using it? You are inserting artificial facts in there to support your argument.
In any event, that still doesn't mean your enemies have it overnight, especially a whole culture.
3) Given you keep modifying the scenarios away from the narrative I'm using with artificial evolution of the enemies, I'm not surprised.
4) If we're talking gunpowder, the raw elements of charcoal, sulfur, and saltpeter are NOT hard to procure. They are literally commodities. 'Hard to procure' generally just means 'go to a bigger city, you're exceeding the wealth cap'. If the base rules don't call out going on a quest for rare elements, they, like material components for spells, are considered to be easily available. It's the default rule. You don't have to go on quests for materials to make tindertwigs, which are basically tiny versions of the same thing.
i.e. the standard rule is that unless it has unique/extremely rare comps, you can just buy them. And if it's actual gunpowder, that's truth.
5) Not at all. The wizard doesn't have to haul around gunpowder at all, and can unleash several fireballs at will from a great distance away, doing more damage then gunpowder and so killing people, and then do it again tomorrow.
So, considering gunpowder a 'massive threat' when these walking cannons are running around is stupid on its face.
Gunpowder's ability comes from the fact you can build up an arsenal of it, and unleash it all at once, AND from the fact it gives a non-spellcaster a KABOOM ability. It takes a much longer time to make bullets than to shoot them, after all.
Note the OP is Players getting unlimited blackpowder access. Building up a stockpile for use in situations is how you use the stuff... and means that when needed, you can get more fireballs/day then a wizard, and all at once, too. that's how wars are basically fought.
6) Because not everyone is a Caster or level 18? CoDzilla is high-end power. Gunpowder is low-end power. A level 1 can light a fuse and launch a keg! True Ubah powah!... oh wait, we just call that a grenade in modern day, ignoring how awesome it would be in a magical world to have your own fireballs as a non-caster.
7) 8) Alchemist in PF, artificer in D&D, and other systems generally have magical alchemists in some form or another, too. The balance issues with gunpowder are still there... it's a world-changing advance in technology for a good reason, after all.
Assuming they're using the stuff in the DMG, then a keg will deal 7d6 damage.
And will take 50 days of downtime to craft.
Each.
If the players can manage to maneuver a wagon-load of explosives worth a few thousand gp to a position where they can leverage it into overwhelming a single tough encounter, that sounds like a worthwhile encounter in itself.That's just it. One thoughtless mention of, "What's in the ship's magazine? I dunno. A dozen kegs of black powder I guess?" and your campaign is facing down a 120d6 crater. It might makes sense for a pirate ship to have a reasonable amount of boom, but that raw damage can get out of hand if you're not careful.
You couldn't fit a cannon in a BoH, as it's dimensions are 2'x4' internally. Also, it only holds up to 500lbs, and cannons usually weigh considerably more than this.I wonder if you could put a cannon in a Bag of Holding or other portable extradimensional space, and then aim and fire it with only the muzzle extending from the bag?
Seems like a more practical way to weaponize gunpowder in D&D than carting barrels of powder around.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.