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I'm a new DM of D&D 4e and I'm looking for some advice for handling failed and fumbled information rolls.
I am using a house-rule that allows for misinformation when a 1 is rolled on the knowledge check.
I think the game system is probably less relevant, i am more interested in player knowledge vs character knowledge.
Let's say the player does a nature check, to find out if a monster (let's say a Troll) is weak against fire: he rolls the dice and fumbles, so since he fumbled I would tell him that he is very certain that this Troll is immune to fire.
For the character this might make sense, but the player knows that he fumbled, so he can assume the opposite, right?
I am not sure what is the right way to handle this situation. What should I tell the player, who obviously knows that he fumbled for his character?