What exactly is common knowledge

[PrinceZane]

My players are very well minded with the various npcs in the MM and such and it has caused a little chaos at times.

On 2 separate occations we've argued over aspects and I ruled their favor just to stop the argument, however, I'm thinking that might've been the wrong thing to do. The first situation was the party coming across a mummy, and the wizard said, "Wait, mummies are undead and have certain things they're immune to." I think anyone that has come across undead a few times would figure this out, but it was their first undead encounter. Their argument was that "everyone" knows undead are immune to poinsons, etc.

The second time was during a dragon battle. They came across a red dragon and instantly started throwing their weaker cold spells instead of high powered fireballs and such. I asked if that is indeed what they would do and they said yes, because dragons are so widely known in the world that everyone knows the basic things to do in an encounter, etc.

We almost settled on a check of some kind to do so, but I couldn't think of an appropriate DC so I just let it go. Any ideas?

 

[punkorange]

I would personally say that would be up to you and your game world. If you wanted, you could make them roll a knowledge check to see if they even know what undead are.

Also, just because you have heard about something, doesn't mean its true. Take the real world, if you come accross a bear and cuddle up in the fetal position, does that mean your safe? I would say common knowledge in your world and the truth behind it would be up to you as the DM.

 

[Lord Foul]

We use knowledge skills in our group for things like that. As for undead, a knowledge religion ckeck would be used. The Dc is 10 + the creatures base HD. this is a free action. Further checks can be made to figure out vulnerabilitiesand stuff. Only one check per round.

 

[Victim]

I'd have no problem with either of those cases. Once you figure that something is undead, a natural conclusion would be that anything specific to living things (especially of those relating to the type of undead, like people) wouldn't work. Do you expect poison to work on a rock, or do much against a dead body? Actually, I think some poisons do work by liquefying tissue, but that's probably not the normal case.

The archetypical dragon is a firebreather. The ideas that creatures wouldn't be hurt by their own attack form and might be weakest against its opposite are pretty obvious.

 

[Patryn of Elvenshae]

I'd have no problem with either of those cases. Once you figure that something is undead, a natural conclusion would be that anything specific to living things (especially of those relating to the type of undead, like people) wouldn't work. Do you expect poison to work on a rock, or do much against a dead body? Actually, I think some poisons do work by liquefying tissue, but that's probably not the normal case.

Agreed, and to continue:

Knowing that Poison doesn't affect the Undead: Knowledge (Religion or Arcana) Check, DC 5

Knowing that some special "poisons" can : Knowledge (Religion or Arcana) Check, DC 25

 

[andargor]

We use knowledge skills in our group for things like that. As for undead, a knowledge religion ckeck would be used. The Dc is 10 + the creatures base HD. this is a free action. Further checks can be made to figure out vulnerabilitiesand stuff. Only one check per round.

Common player knowledge is uncommon character knowledge. I second the above statement, but I will add that it is RAW:

* Arcana (ancient mysteries, magic traditions, arcane symbols, cryptic phrases, constructs, dragons, magical beasts)
* Architecture and engineering (buildings, aqueducts, bridges, fortifications)
* Dungeoneering (aberrations, caverns, oozes, spelunking)
* Geography (lands, terrain, climate, people)
* History (royalty, wars, colonies, migrations, founding of cities)
* Local (legends, personalities, inhabitants, laws, customs, traditions, humanoids)
* Nature (animals, fey, giants, monstrous humanoids, plants, seasons and cycles, weather, vermin)
* Nobility and royalty (lineages, heraldry, family trees, mottoes, personalities)
* Psionics (covers ancient mysteries, psionic traditions, psychic symbols, cryptic phrases, astral constructs, and psionic races. You can use this skill to identify psionic monsters and their special powers or vulnerabilities)
* Religion (gods and goddesses, mythic history, ecclesiastic tradition, holy symbols, undead)
* The planes (the Inner Planes, the Outer Planes, the Astral Plane, the Ethereal Plane, outsiders, elementals, magic related to the planes)

...

In many cases, you can use this skill to identify monsters and their special powers or vulnerabilities. In general, the DC of such a check equals 10 + the monster's HD. A successful check allows you to remember a bit of useful information about that monster.

For every 5 points by which your check result exceeds the DC, you recall another piece of useful information.

So, whatever your players might think is "common knowledge", you are perfectly within the rules if you request a Knowledge check.

Andargor

 

[Odhanan]

I would personally say that would be up to you and your game world. If you wanted, you could make them roll a knowledge check to see if they even know what undead are.

Same opinion here. This is really up to you as a DM, and what sort of setting you're playing with. If monsters are not common place and so on, then the characters do not automatically know what an undead is. You could also decide that, since they are, say, 12th level, the characters should have encountered at least one undead during that time, or none at all.

 

[Kae'Yoss]

As they said: It's the DM's decision.

I don't use the Knowledge rules as written, since it has a few quirks: For example, if you encounter a blue wyrmling, it is far easier to figure out what it is then it is with a great blue wyrm. So if you meet that big blue bastard, you won't know about its electricity, and that it's a true dragon, but with the wyrmling, you can tell, and maybe even more. So the general stuff is often easier with higher CR, because those things are really infamous.

All player characters are considered to know the whole info that you can get out of the PHB, and then some. Stuff like trolls and their fire vulnerability, the main types of dragons and their usual breath weapons and immunities (though this refers to their color, not their shape, so you still can fool someone by giving to him a blue "skull dragon", unless he makes his save and realizes that the shape suggests black rather than blue), a medusa's or basilisks petryfying gaze, the general traits of undead, and stuff like that.


In your case, the undead traits like immunity to crits and sneak attacks, poison and ability score attacks would be known by most people, and all adventurers, they'd also know that red dragons breathe fire and are immune to it, but that cold works better against them.

 

[RedShirtNo5]

The rule of thumb I've used for about 15 years is "Information about monsters in the D&D Basic Rulebook (Holmes edition, blue cover) is common knowledge." In 3e, other information needs a knowledge check.

We've found it to be a useful standard; the blue book includes most of the common monsters of mythology and some D&D staples (e.g., carrion crawlers) that one can assume that the inhabitants of a D&D world would have heard of through stories and rumor. Since the information is from a prior edition, it's often inaccurate and incomplete. And of course as DM I always reserve the right to change the statistics of even well-known mosters. But it provides the baseline for what the characters have heard of.

Naturally, this doesn't help you much if you don't have the blue book.

-RedShirt

 

[Philip]

Common knowledge is what you as DM decide is common knowledge. Not all Red Dragons in your campaign HAVE to be firebreathing cold-hating creatures.

If you are going exactly by the MM all the time, separating OOC knowledge and 'common knowledge' becomes quite hard for most players. Just mix it up now and then.