iserith
Magic Wordsmith
In addition to 2, I suggest making one's game resilient against foreknowledge by building adventures where knowing everything about it doesn't really affect it very much. People play my one-shots repeatedly even knowing what to expect. It doesn't really matter.It seems like there are two general responses to encountering this being expressed in this thread:
1. This unconscionable cheating and such a person should be punished and/or bounced from the table.
2. Considering the reason and context (<-----this part is really important) for why this is happening and trying to determine a way to get everyone on the same page about approach to play and what is appropriate.
Personally, I prefer the second choice. It may end up leading to the first choice anyway, but I like to know motivations and figure out ways forward, if possible.
Or, as I said, creating a disincentive to relying on that knowledge by changing things and telling players you did that. For example, the post about the duergar upthread - that totally wouldn't matter to me. My players know I sometimes change monsters which means that whatever is in the Monster Manual is effectively as good as a rumor their characters heard in a tavern, which is to say unreliable at best. The smart play in all cases is to verify assumptions before acting on them. If the players are smart, they'll do that, which means they're effectively playing the same way a player without that knowledge might.