I’ve been going over my ideas for my campaign setting again, this time specifically with a look at what kinds of reactions and emotions I want to evoke in the players. (Something I’ve read here, but never consciously gave much of a thought before.) Some themes I want the setting to encourage are trusting in what you think is right, and always questioning what hidden motives both enemies and allies may have.
And that of course means that NPCs will be lying a lot. Which interestingly, villains in fiction rarely do. When an enemy gets defeated and cornered and the protagonists start to question him, he usually will just tell them everything he knows, the heroes take it as truth, and it all turns out to be completely correct in the end. Players will probably not expect that NPCs will lie to them, which is good. But it also means that you can’t simply copy things you’ve seen before. So using lies in RPGs is something that can use a bit additional thought.
Now, one very important thing to remember is that an RPG is not just the actions that happen to the characters in the game, but often even more importantly also the interaction between the players, which includes the GM. Unless you’re a terrible person, you don’t want the players to be angry at you, but at an NPC who fooled them. And at the same time applaud you for playing things so well.
As GM, you’re not only the eyes and ears of the PCs, you are also to a great extend all their background knowledge about the world around them. The GM filters everything that’s going on before telling it to the players, by not only deciting what things are important, but what the players and the PCs would consider important. Everything has already been interpreted by the GM, who only tells the players what he wants them to notice. If you’re a really good GM, you can describe things in a way that may look unimportant but still stick in the players minds and minimize any bias, allowing the players to make their own interpretations and conclusions. But even then you still have the ability to make the players believe anything you want them to believe. Even if the players have not consciously been thinking about it, they still understand at some level that they depend on the GM to get an accurate mental picture of the world, with which they can draw the right conclusions or make wrong interpretations. So I think the subject of decieving the players is something that should be treated with extra care. Making a big mistake in a game can be a lot of fun. Feeling that you’ve been set up to do something that you could not have possibly avoided, but still get blamed for is probably the worst thing that could happen in a game. If in any way possible, avoid this from happening.
That being said, I have three ideas how to make lies in RPGs work without making the players feel abused by the GM:
Straight Lies: Let an NPC say something that is just straight out false. Not just mostly wrong, but a complete fabrication. For example, tell them that a passage has no traps, an item will prevent a monster from attacking, a key can open a lock, or the location where a special item is stored. When the PCs get there and try to use the information, it’s immediately clear that the NPC lied to them. Nothing ambigous. They took his word for it, even though they shouldn’t. The GM didn’t pull any mean tricks, he just played the NPC as he should have, and it’s the players fault for just trusting him. No bad blood here, and the players will learn to not take things at face value in the future.
Tell the truth, but make it work for the villain: Even if the players get the information they are asking for, it doesn’t have to be the information that they actually need. Probably a bit difficult to pull off, since it depends on what exactly the PCs will be saying to the NPC, but he might even give them additional details in an attempt to trick them into doing something that will benefit him. For example, if the players ask from whom they can get a key, the NPC could direct them to one of his henchmen who already betrayed him. The PCs get what they wanted, but the NPC benefits from it as well.
Avoid Jedi-Truths: No, “what I told you was true… from a certain point of view.”, is still a lie. That line is one of the most infamous from Return of the Jedi, and rightfully so. However, Obi-Wans real mistake was not to tell the lie. But to deny that it was a lie even after the truth came out. Yes, an NPC might make such a claim because the NPC is a terrible person and the GM does not share that view. But will it really ever feel that way to the players? You just can’t help but feel that the GM played you by telling everything in a way that would only allow you to think it was the truth. Unless you feel really super-sure about it and it’s an NPC that has already been well established as a terrible person and constant lier, I’d say avoid this entirely.