How much does a player know about a spell affecting his PC?

Question

On a West Marches style Pathfinder server my PC was fighting an undead sorcerer that cast a spell on my PC. The GM described the spell as follows:

There is a dark whip thing that goes around your neck and drains your strength.

So I found the spell the spell limp lash online. (I know that's metagaming, but in my normal Pathfinder experiences this isn't viewed as bad form.) And, when I read that the spell could be sundered, my PC sundered it, and the GM got angry.

My question is this: If my PC were unable to identify the spell as it was cast and unable to identify the spell in place, does my PC know anyway that he can sunder the limp lash spell, or am I, the player, left guessing at how (or even if!) my PC can free himself from the spell?

More broadly, if an utterly mundane yet wholly nonstandard exception exists to handle a situation, does the GM reveal that exception? Or is such knowledge nominally secret, only available to a PC through class features and the like or through trial and error? For example, does a PC that's fighting a hydra know that sunder attempts can be made against a hydra's heads despite the fact that the combat maneuver sunder can't usually target a foe's head?

Answer 1

No

There is certainly no rule anywhere (barring the rules options you mention) that the GM needs to tell you anything about the behavior of spells (or monsters, or...), and they usually won't, so the real question at hand is "well but can I look it up/know it myself?" We will proceed with that new question.

It Depends

While by the Pathfinder rules, there are specific ways to learn about spells, the rules themselves are silent on the acceptability of meta-gaming - the acting on player instead of character knowledge about monsters, spells, and so on.

This ends up being a playstyle decision that different groups see differently. Unfortunately, they don't always bother to say it out loud because everyone thinks "their experience" must be normative. And also, this is a topic groups tend to feel strongly about.

No Metagaming

Many groups explicitly or tacitly expect no metagaming, or at least for your metagaming to be politely concealed. Gaming groups with more of a focus on immersion, world exploration, acting in character, etc. may tend towards this expectation. "Your character wouldn't know that" and acting plausibly in the game world is more important than "winning."

Note that in this case the GM isn't going to tell you what the e.g. spell does because your character doesn't know it.

Metagaming's Fine

Many groups are fine with metagaming. Although "looking it up at the table" may stretch even these groups' patience, gamist-oriented playstyles often consider "player ability" via knowing these things to be a key part of the game and tolerate or encourage metagaming. "Winning" is more important than other concerns.

Note that in this case the GM isn't going to tell you what the spell etc. does because that's cheating and making it easy for you; you need to up your game and read the books more.

Mixing It?

Unfortunately, there's not a lot of options in the middle here, and groups that have some people doing one and some doing the other will tend to fight about it. Some folks metagaming disrupts the non-metagamers' fun more than the other way around, so arguments around this get heated.

In shared campaigns like Pathfinder Society, it's impossible to stop people from doing it, so it tends to have at least some metagamers in it. As a result most PFS play isn't very simulationist or narrativist. (Those wishing to complain about my use of GNS terminology can direct their concerns to /dev/null.)

However, a lot of older edition play - like a West Marches campaign might tend towards - is much more invested in exploratory play and can have a dim view of metagaming.

But then how?

Then how the heck do you ever know to sunder a limp lash or cut off a hydra’s head or use shatter on a demilich? Aren’t these an insoluble trick problem? No. One, your character could be trying out of the box solutions more generally. Does that seem kinda da solid? Maybe you can hit it... but it’s also an opportunity to play smarter. Research opponents. Ask somebody. “Hey magic sage I got choked out by this black energy whip what could I have done about that?” Also, if you are a fighter without high Spellcraft, maybe a party member should be making those checks and helping you out... Old school sandbox campaigns (like West Marches style) often want you to do real in-world problem solving and consider looking it up lazy cheating.

TL;DR

So you should have a discussion with your group about the appropriateness you all find for metagaming so that you all have a happy agreement.

Answer 2

The character knows as much as the GM tells the player, or allows the player to research.

You mentioned Spellcraft and Knowledge checks. Those two describe all your character knows. Depending on the table, the GM might allow the players, either explicitly or implicitly, to know and use more information (such as "there exist a spell that protects you from energy damage" or "resurrection is possible for high-level characters"), but it's the GM's call and table consensus how much information is available if not explicitly given by the rules.

In this case, there is no source that you have to justify knowing that information, and the GM reaction makes it clear that it was not considered "general knowledge".

On created effects

Limp Lash creates a specific effect, that is, a dark whip-shaped field of energy. It is a valid argument to consider that any created effect can be recognized as such, and some or all of their properties (can be sundered, limited range, can pass through walls...) be recognizable by any creature, even if they have no knowledge of the spell.

The same argument applies to the hydra example. Suppose you have learned that destroying all and hydra's heads kills it, how can you know that you need a sunder attempt ? Simple answer, you don't.

Named actions, especially combat maneuvers, only codify some objectives you want to achieve in combat. In the most general case, the GM should tell you what to roll after you have declared your intention (such as "I sever the whip" or "I cut the head") -- although for many simple and common actions, this is bypassed by the players directly rolling whatever is appropriate.

To summarize : you should ask your GM what your character can do against any effect that is visible, but that your character might not have full knowledge about. If you have a doubt, express an intention rather than an action.

Why the GM got angry in this situation

In this specific case, I don't think the problem was that you requested to make a sunder attempt against the whip. However, the GM gave you limited information, then you went ahead to gain more knowledge about it, and acted on this (clearly meta) knowledge. I guess the GM felt like you were using meta-knowledge to compensate for something your character failed to learn voluntarily, which was the problem.

In general, attempt to separate player and character knowledge, and ask before acting. Usually, people reading the rules isn't such a big problem for GMs, as long as the separation is made clear.

At my table, I avoid this kind of problem by directly asking the GM : "I read that the whip can be sundered ; is it visible, obvious to my character, or should I have succeeded on my spellcraft check to notice that ?" If your GM is similar to mine, this would be a good way to avoid repeating this situation in the future.