Trolls and Fire

The question of metagaming has raised its ugly head on ENWorld once again, and once again the inevitable example of trolls and their weakness to fire has been raised, with the endless back and forth about whether an experienced player with a newbie character should know about the fire.

The unfortunate consequence of which is that people have proceeded to argue the example rather than the issue - because trolls are such a common monster, ever D&D player who has even a little experience knows about them and fire. So a DM who uses that as some sort of a 'reveal' is basically copying George Lucas' great 'reveal' that Anakin turns into Darth Vader in RotS - it's basically the single best-known spoiler in film history, so it's not going to have much of an impact.

Basically, if a DM wants to use trolls in an encounter, he should start with the assumption that the players know about the weakness to fire. From there, he can go one of two ways: either he can build his encounter assuming that they'll use that knowledge (in which case he should treat the trolls as any other "big bag of hit points" monster, to be battered into submission) or, better, he should structure the encounter so that using fire is a judgement call - maybe the fight occurs in a cave filled with exlosive gas, or something. And that way the players get to choose between several imperfect solutions to their problem. Simply pitting experienced players against trolls and expecting them to pretend not to know is madness of Star Wars prequel proportions.

But there is a bigger issue as regards metagaming. (Which is defined in this particular debate as the use of player knowledge to bypass character knowledge, which itself is a case of definition drift. But never mind.) What if the example isn't the classic trolls/fire example, but something more extreme? What if the player has read the adventure and "just happens" to look for treasure in all the right places? What if the player is a former DM with the MM memorised? Heck, in an extreme case, what if the player has all the books on his phone and is looking them up in-game?

Ultimately, I think it boils down to a very simple answer: don't do that.

Basically, players should endeavour to play their characters in good faith (which is a usefully vague term). And, yes, the DM should seek to throw a few changes their way so that simply looking at the books won't help so much - use some custom adventures and/or custom monsters, mix up some of the encounters or treasure locations, or something of that ilk.

And when all else fails, it's probably better to embrace the metagame rather than try to fight it - know your players' levels of experience and build accordingly, so that applying that knowledge leads to something more interesting than simply pretending that they don't have it.