DM lying to players

[Silus]

With me being the DM in this situation.

So here's the short of it. Running a game with a world with "no magical creatures" (dragons, chimera, fey, etc). It's one of those things that I'll emphasize to the players every time they bring it up. Of course I'm lying through my teeth and plan to throw some "magical creatures" (see: Werewolves) at the players in a "Yeah, the world if more complex and strange than you thought it would be". Not out of the blue mind you. There'd be some buildup to the whole "Surprise! Werewolves!" thing.

As a player, would you or would you not be upset if the DM had been all but swearing up and down that there are nor supernatural creatures, only to throw a pack of werewolves at the party?

[Kyberwulf]

I don't know. Does that extend to no magic at all? Because if there are no magical creatures, that means that the players really don't have any idea about any weaknesses the monsters have.

How would a world with no magical creatures exist with magic in the world.

[Geordnet]

Yes.

I wouldn't be so mad if you had said something like "they exist in fairy tales", avoided the subect, talked around the issue, et cetera. Exactly what you can say will depend on your setting, though.

[Barsoom]

I'd say it's a nice twist. However, "know your audience" caveat applies.

[Geordnet]

How would a world with no magical creatures exist with magic in the world.

The same way you can have sci-fi wihout aliens.

[Silus]

I don't know. Does that extend to no magic at all? Because if there are no magical creatures, that means that the players really don't have any idea about any weaknesses the monsters have.

How would a world with no magical creatures exist with magic in the world.

Regular magic (probably a tad heavy on the arcane side). And....I dunno, there just aren't typical magical creatures. Sure, some cryptids (yeti, sea serpent, etc) may exist, but big city destroying things like dragons and the like don't because....*Shrugs* They just don't. Killed off en masse I suppose. Driven to extinction then forgot about. Faded into legend or something.

The general way I'd try to handle the whole werewolf thing would be something like this:

"While you're at the bar, a dwarven woodsman stumbles in, covered in blood and a little drunk. He's babbling about 'Wolf men' in the woods and seems half deranged. A few bar patrons help the dwarf to a table and fetch him a beer."

"The centaur barman shakes his head and looks to you (the players). 'Pay him no mind. Local legends and whatnot. Everyone 'round here knows that the wolf-man legends are just that. Legends.'"

Yes.

I wouldn't be so mad if you had said something like "they exist in fairy tales", avoided the subect, talked around the issue, et cetera. Exactly what you can say will depend on your setting, though.

Well there'd be some buildup to it, not just dropping it out of left field. This would take place in the campaign fairly early'ish, before the players start delving into the weird and hidden magical side of the world (Sphinx archivists, colossal intelligent undead owl oracles, fey empresses, etc.).

[valadil]

Depends on what the GM said exactly. I think I'd object to "I want to run a game with no magic," but not to "I want to run a game set in real world England circa 1800."

It also depends on who the GM is. I know some GMs who would run a no magic game, just so their NPCs could be the only ones with magic. I know others who would run it that way because they wanted their players to feel the surprise their characters felt. I try to only play with the latter type of GM, but if the former pulled this kind of stunt I'd be upset.

[Silus]

Depends on what the GM said exactly. I think I'd object to "I want to run a game with no magic," but not to "I want to run a game set in real world England circa 1800."

It also depends on who the GM is. I know some GMs who would run a no magic game, just so their NPCs could be the only ones with magic. I know others who would run it that way because they wanted their players to feel the surprise their characters felt. I try to only play with the latter type of GM, but if the former pulled this kind of stunt I'd be upset.

Well the world is:

-Low Fantasy: No mythical monsters or creatures (fey, outsiders, abberations, dragons, etc).
-High/Low magic: High arcane, Low Divine (Divine casters are allowed, they’re just less prominent than arcane casters (Druids are far more common than clerics though)
-Medium technology: The overall tech level is around the Industrial period (steam and coal power being “things”)

'Course the "Low Fantasy" bit is a lie. In-game conventional wisdom, even un-conventional wisdom outside of really, REALLY old creatures states that dragons, fairies, and werewolves are nothing more than myth and legends told to entertain and frighten.

[atomicpenguin]

There is only one instance I can think of where that would be bad: if there are any substances or weapons that would have an advantage over magical creatures that they didn't buy because you told them they wouldn't need to fight any magical creatures and you then have them fighting magical creatures all the time. That'd be like saying "you don't need to put points in swimming because the campaign takes place in rural colorado", then magically teleporting your party to oceanworld in the first session. This is intentionally misleading your party so they will be worse off in your campaign when, under normal circumstances, they should have been way better off.

But this doesn't seem to be what you're doing. What you're doing is saying that, officially, something shouldn't exist so that when you do produce magical creatures that it has the higher shock value that it should in the world you've created. But there are ways you can do it right. Firstly, you shouldn't just say they don't exist if you can avoid it. This is outright lying to the players and, even though its for a good cause in this case, your players may resent it later. Instead, have a character in your world tell them that or, if you are speaking as the GM, say things like "No one has ever seen anything like that in my world" or other statements that convey that as far as anyone knows magical creatures don't exist. This is technically true, because your NPCs genuinely do believe this.

Also, if you can, read or watch Game of Thrones. George R.R. Martin does a great job of introducing magical concepts with the caveat that they don't really exist anymore, filling the plot with mundane occurrences that have nothing to do with magic and in some cases could include magic but don't, then coming out of left field with something crazy and weird that must be magical. Its all about the pacing. Make your characters do a bunch of mundane missions to make them forget about the issue of magical creatures, then one day, Wham! the villain is a werewolf or using werewolves! Also, when you tell them this, give them a minute or two to react to this. This will hopefully generate the shock of seeing something that shouldn't happen that you're going for.

[Doug Lampert]

With me being the DM in this situation.

So here's the short of it. Running a game with a world with "no magical creatures" (dragons, chimera, fey, etc). It's one of those things that I'll emphasize to the players every time they bring it up. Of course I'm lying through my teeth and plan to throw some "magical creatures" (see: Werewolves) at the players in a "Yeah, the world if more complex and strange than you thought it would be". Not out of the blue mind you. There'd be some buildup to the whole "Surprise! Werewolves!" thing.

As a player, would you or would you not be upset if the DM had been all but swearing up and down that there are nor supernatural creatures, only to throw a pack of werewolves at the party?

I'd be upset, you can lie to my character, but not to me. Seriously, I do my best to maintain character/player separation. This means when you lie to me you are lying to me. My character can be given all the false information you want to give him, but he is not me.

Do you WANT your players to maintain player/character separation and to not metagame? Then DON'T lie to the players to support a missunderstanding that the CHARACTERS have. You are either (A) deliberately encouraging metagaming by destroying the very idea (that the character and player are separate things) that prevents metagaming or (B) deliberately lieing to the PLAYERS, not characters about the rules of a game they are playing.

Which of these is a good idea?

[navar100]

Yes

It means I can't trust you. If I can't trust you, I question every decision. If I question very decision, I don't get to enjoy the game.

[Silus]

I'd be upset, you can lie to my character, but not to me. Seriously, I do my best to maintain character/player separation. This means when you lie to me you are lying to me. My character can be given all the false information you want to give him, but he is not me.

Do you WANT your players to maintain player/character separation and to not metagame? Then DON'T lie to the players to support a missunderstanding that the CHARACTERS have. You are either (A) deliberately encouraging metagaming by destroying the very idea (that the character and player are separate things) that prevents metagaming or (B) deliberately lieing to the PLAYERS, not characters about the rules of a game they are playing.

Which of these is a good idea?

*Nods* I understand. The werewolf thing was actually an afterthought, a way to pad an already depressingly thin campaign (or at least add in more substance to those "going from point A to B" bits). The whole "there are no magical/mythical creatures" thing was established to 1) help explain how the tech level is around Industrial levels, and 2) to keep the players from making insane characters.

Now if I started hinting at the existence of these mythical elements early on, would that be better than springing something lie werewolves on the players? For example, the players are gonna start in a village near a sort of Black Forest type forest. Maaaaaassive forest stretching for tens of miles. Maybe drop hints of monsters of fairies in the woods that, hopefully, the players will discount as nothing more than rumors and such.

[Deepbluediver]

I think I see the issue here: Tabletop gamers can get kind of jaded experienced over time, and something that should evoke shock and awe becomes mundane and humdrum.
Werewolves? AGAIN? Oh well break out the silver and fire.

So the DM is, I think, trying to bring some of the shock and surprise and excitement back into the game. (correct me if I'm wrong)

That being said, while lycnathropy is labeled as a magical disease in D&D, it doesn't have to be, and werewolves are not (I think) normally considered an inherently magical creature. They are typically classified as human(oid) with either a subtype or a template.

So rather than saying "no magical creatures", a better way to phrase it might be: the following creature types do not exist: dragons, fey, elementals, outsiders, whatever else you want, etc. Also, there are no intelligent humanoid races other than humans.
Which makes for a perfectly viable game world, without needing to "lie" to your players.


As several other people have said, your group's reaction will depend largely on the group, which you know better than the rest of us. If it where me and some one mentions "Wolf Men" then werewolves are the first thing that comes to mind no matter what else the DM might have told me.
Either that or its just bandits in funny costumes.


If you really want to surprise and/or confuse your players, a better option might be to do the "Our X are different" trope. Cultured and sophisticated orcs, savage and barbaric gnomes, mechanically inclined elves, etc, which keeps players on their toes but won't trap you with your own words.

[Coidzor]

With me being the DM in this situation.

So here's the short of it. Running a game with a world with "no magical creatures" (dragons, chimera, fey, etc). It's one of those things that I'll emphasize to the players every time they bring it up. Of course I'm lying through my teeth and plan to throw some "magical creatures" (see: Werewolves) at the players in a "Yeah, the world if more complex and strange than you thought it would be". Not out of the blue mind you. There'd be some buildup to the whole "Surprise! Werewolves!" thing.

As a player, would you or would you not be upset if the DM had been all but swearing up and down that there are nor supernatural creatures, only to throw a pack of werewolves at the party?

Yeah, you could have communicated that idea to the players without having to directly lie to them. Ambiguity is your friend. So, yes, I'd be upset at the DM for violating the compact of trust about when deception is acceptable as part of the game and when the DM is not to act with deception because we're not actually playing the game when the deception is made.

[Silus]

I think I see the issue here: Tabletop gamers can get kind of jaded experienced over time, and something that should evoke shock and awe becomes mundane and humdrum.

So the DM is, I think, trying to bring some of the shock and surprise back into the game.

That being said, while lycnathropy is labeled as a magical disease in D&D, it doesn't have to be, and werewolves are not (I think) normally considered an inherently magical creature. They are typically classified as human with either a subtype or a template.

Well the idea is that the players would encounter the werewolf/ves in the northern reaches of the world where there's an increasing amount of magical radiation (outright rumors of Winter Wolves at the north pole for example). Likely gonna treat lycanthropy as a curse if anything. Or I'll just take a wolf and tack on the Manimal template to it and use that.

If you really want to surprise and/or confuse your players, a better option might be to do the "Our X are different" trope. Cultured and sophisticated orcs, savage and barbaric gnomes, mechanically inclined elves, etc, which won't trap you with your own words.

Already doing that =P

Drow are a race of mad scientists that use magic to dabble in genetics, Orcs take after the WoW noble shamanistic savage, and Centaur kinda bounce between tribal and city dwelling.

Yeah, you could have communicated that idea to the players without having to directly lie to them. Ambiguity is your friend. So, yes, I'd be upset at the DM for violating the compact of trust about when deception is acceptable as part of the game and when the DM is not to act with deception because we're not actually playing the game when the deception is made.

What I'm worried about though is that the players see through the deception. They are, in all probability, more experienced than I am and therefore more genre savvy. I understand that they'll likely keep up the IC/OOC separation, but I still want to try legitimately shock/surprise them the first time one of these supernatural things shows up.

I'm worried that dropping too many hints will have the players going "Ok, he's dropping hints, so there's a chance that he's gonna throw this stuff at us in the future". Next thing you know, they'll be buying silver weapons "just because" or something

[TheStranger]

I don't know if it's early enough in this campaign to do this, but you could have the "no magical creatures" thing play out in-game instead of just telling your players.

What I mean is, you do your worldbuilding such that people may believe in dragons, goblins, or whatever, but all "reasonable" people know that these are just stories - folklore, but not something that educated people believe in. Then you build on that by having a couple adventures where your players investigate something that looks like a vampire attack, and that all the villagers are insisting is a vampire attack, only to find out that the "vampire" was really Old Man Withers in a mask. Throw a couple of those at your players, then have an actual werewolf start killing people.

[Geordnet]

Regular magic (probably a tad heavy on the arcane side). And....I dunno, there just aren't typical magical creatures. Sure, some cryptids (yeti, sea serpent, etc) may exist, but big city destroying things like dragons and the like don't because....*Shrugs* They just don't. Killed off en masse I suppose. Driven to extinction then forgot about. Faded into legend or something.

The general way I'd try to handle the whole werewolf thing would be something like this:

"While you're at the bar, a dwarven woodsman stumbles in, covered in blood and a little drunk. He's babbling about 'Wolf men' in the woods and seems half deranged. A few bar patrons help the dwarf to a table and fetch him a beer."

"The centaur barman shakes his head and looks to you (the players). 'Pay him no mind. Local legends and whatnot. Everyone 'round here knows that the wolf-man legends are just that. Legends.'"

Hm, it seems that you're going back on yourself here. I don't know about anyone else, but I would classify both dwarves and centaurs as "magical creatures".


You shouldn't worry about surprising the players so much, methinks. Lying about traditional monsters might work for the first encounter, but it's more likely to end in bad feelings. Either way, once the dam breaks, they'll go back to expecting everything again.


I think a better idea would be to subvert the natural expectations of the players. Tell them that all traditional monsters exist in myth, even when they ask if they exist in (in-verse) fact.

But then, when the players (and PCs) think "werewolf", throw in a new twist. Make the werewolf the Cŵn Annwn instead (or at least a "backwards" werewolf). Make it so that the full moon is their weakest moment, because it drives them crazy. When they bring silver weapons, have them find out it they're worthless without the right protective runes. When they go seek out a wizard for the runes, have them turn out to be just shapes that anyone can draw.

If you want to really surprise them, you'll have to get creative.

[Silus]

I don't know if it's early enough in this campaign to do this, but you could have the "no magical creatures" thing play out in-game instead of just telling your players.

What I mean is, you do your worldbuilding such that people may believe in dragons, goblins, or whatever, but all "reasonable" people know that these are just stories - folklore, but not something that educated people believe in. Then you build on that by having a couple adventures where your players investigate something that looks like a vampire attack, and that all the villagers are insisting is a vampire attack, only to find out that the "vampire" was really Old Man Withers in a mask. Throw a couple of those at your players, then have an actual werewolf start killing people.

Hmm...

That...

I actually think I'll do that I need to pad the first three or four levels out before the big bad shows up anyway. They'd probably get to the werewolves by level....5-6? There's gonna be like 6-7 players and I've all but outright suggested they pick up the Leadership feat...

You shouldn't worry about surprising the players so much, methinks. Lying about traditional monsters might work for the first encounter, but it's more likely to end in bad feelings. Either way, once the dam breaks, they'll go back to expecting everything again.

The idea is that the werewolves will be a sort of wakeup call in the "monsters do exist" kinda way.

I mean, they're going off to a huge druid controlled world tree city to meet an oracle that turns out to be a Gigantean Awakened Giant Owl Lich Oracle to get info and directions to three other sites, one of which is the den of a Sphinx (likely the last living one) and eventually to an underground location to stop a Denizen of Leng from using a lost Cubic Gate to rip open the planar barrier that's locked down the world so Leng has a direct passage for slave taking. And the tearing down of the barrier sets off a planar beacon that attracts extraplanar entities to the fresh, ripe world of unclaimed souls.

[Splynn]

I wouldn't be upset at all. Hell, I would even applaud the move, since you're starting to tinker with the setting you've created and that usually produces the most interesting stories.

The role-playing part of this is what should be more fun. Even to the players; not just the characters. Star Wars: Empire Strikes Back wouldn't have been nearly as fun if, every time Luke mentioned Vader, someone said "btw, Vader is Luke's dad. You're not supposed to know this, but we don't want to lie."

Not only is that idea ridiculous, it's crap storytelling. Roleplaying should be telling a story just as much as allowing the players to overcome obstacles such as werewolves.

It's not about whether or not the players would allow the information to affect their decisions; it's about having a surprise in the story. This is no different than having a major villain be the father of one of the characters and not telling them until the reveal.

The one thing you ABSOLUTELY have to do, though, is make sure that the group has adequate resources once they do go monster-hunting. If they go after a werewolf, they should be able to roll "gather information" or knowledge checks in order to decide what the weaknesses of such creatures are. And then they should be able to procure the items.

If you don't allow that then you are probably just making the fight more annoying than it should be, and setting the group up for failure. That is where this turns from storytelling to sabotaging the group; avoid that line.

[Silus]

The one thing you ABSOLUTELY have to do, though, is make sure that the group has adequate resources once they do go monster-hunting. If they go after a werewolf, they should be able to roll "gather information" or knowledge checks in order to decide what the weaknesses of such creatures are. And then they should be able to procure the items.

If you don't allow that then you are probably just making the fight more annoying than it should be, and setting the group up for failure. That is where this turns from storytelling to sabotaging the group; avoid that line.

Find some silver weapons in the cabin they're holed up in alongside an Apocalypse Journal mentioning how "the wolf men don't seem to care for the silverwear I shot at them. That might be the way to bring the beasts down"?

[Splynn]

Find some silver weapons in the cabin they're holed up in alongside an Apocalypse Journal mentioning how "the wolf men don't seem to care for the silverwear I shot at them. That might be the way to bring the beasts down"?

Yea, that'd work fine. Or, for example, if it's trolls, then perhaps have the fight start in a dry part of the forest, then lightning strikes a tree and now there's a source of fire.

The troll seems particularly concerned about the fire.

You don't have to hand stuff to them directly, but you do need to make sure that your players can handle what you're throwing at them. What you've just described should work more than great. Even only one silver weapon is enough. Just don't handicap your players for the purpose of storytelling.

[Darius Kane]

I wouldn't believe you. If there's magic, there are bound to be magical creatures. If you would say "There are no magical creatures" I would say "Why you lying, bro?"

[Coidzor]

I wouldn't be upset at all. Hell, I would even applaud the move, since you're starting to tinker with the setting you've created and that usually produces the most interesting stories.

The role-playing part of this is what should be more fun. Even to the players; not just the characters. Star Wars: Empire Strikes Back wouldn't have been nearly as fun if, every time Luke mentioned Vader, someone said "btw, Vader is Luke's dad. You're not supposed to know this, but we don't want to lie."

Wrong way of thinking about it. Obi-Wan used weasel words to dodge the issue. This scenario is more like if Luke had point-blank asked Obi-Wan if Darth Vader was his father and Obi-Wan point-blank said no with no room for ambiguity.

[TinyHippo]

If you tell the players (players, not characters) something, it should be the truth. If the DM changes the rules of the world, that breaks trust in the DM. It would for me, anyway.

[Deepbluediver]

@Silius

It might help if you gave us more background on the starting scenario and the long-term goal for this game.

For example, if the players start of in a magic-creature-less land, and have several adventures without seeing a single dragon scale or tuft of werewolf fur, then the slow introduction of new species of the ramping up of magical effects can make for a very interesting campaign.

If the story starts out like "You all meet in a tavern when werewolf victim #1 tumbles through the door..." then at best your players will wonder what the point was. And the implications for your style of DMing are not very good.


If you want to set the stage a little bit, rather than declaring something like "no magical creatures", just TELL the players that, up until this point, most people think that stories of magical creatures are just that: myths and legends. And while your players may know whats going on, no NPC will believe them. You can set up a scenario and if your players are decent people they should go along with it, but at all costs I think you want to avoid any statements you know will be outright false.

[Silus]

@Silius

It might help if you gave us more background on the starting scenario and the long-term goal for this game.

For example, if the players start of in a magic-creature-less land, and have several adventures without seeing a single dragon scale or tuft of werewolf fur, then the slow introduction of new species of the ramping up of magical effects can make for a very interesting campaign.

If the story starts out like "You all meet in a tavern when werewolf victim #1 tumbles through the door..." then at best your players will wonder what the point was. And the implications for your style of DMing are not very good.


If you want to set the stage a little bit, rather than declaring something like "no magical creatures", just TELL the players that, up until this point, most people think that stories of magical creatures are just that: myths and legends. And while your players may know whats going on, no NPC will believe them. You can set up a scenario and if your players are decent people they should go along with it, but at all costs I think you want to avoid any statements you know will be outright false.

Well the "no magical creatures" thing was, at the time, a sort of catch all where the players wouldn't be asking if X creature existed (Kobalds, oozes, dragons, demons, etc).

The campaign is gonna run like this (with some variation, sandboxing and more than a heaping helping of improvisation).

Spoiler

Show

Players meet up and preform some odd jobs until about level 3-4 (Backstory, establishing character personalities and inter-party dynamics, bounty hunting, exploring, etc). When they get to the city Tamaria at the edge of the Black Forest esque Fairywood, a sort of magical SETI like research station explodes (The station is attempting to contact the "outside" that lies beyond a several millennia old planar barrier). They players rush in, maybe save some lives, and come across a being that'll be called "The Denizen" (A Denizen of Leng Summoner which breaks all the stablished rules about summoning and extraplanar creatures due to him essentially sledgehammering his way through the barrier). A little later, the players get called upon by a person known as "The Queen", the benevolent ruler of Tamaria and the Fairywood.

Players go meet her, tell her what happened. It's likely gonna be obvious that she knows more than she's letting on. She sends the players north to Calastiss, a druid controlled city inside the base of a massive World Tree up in the magically rich Northern Reaches (Basically Canada/Russia). Players get there, meet with the government, find out that they are to see the oracle that lives high in the boughs of the tree. Players travel up and find that the oracle is really a massive undead owl (In a rather shameless shout out to Secret of NIMH). The owl tells the party that bad stuff is going down and that there are three locations they must go to to get all the knowledge they'll need to combat the rising threat: A temple on a desert/jungle peninsula for the location of where the Denizen is headed, a lost library in a desert canyon to what the the Planar Barrier is, what the Denizen plans to do, and what will happen if the barrier is dropped, and lastly to a mountain monastery to learn just what the Denizen is and how to kill him permanently.

After that they have to travel to the industrial city of Bastion to head underground (there's a train) to the Drow city of Markibyr. From there, they descend to the lowest caverns of the world to locate a lost and partially sunken city that holds the only remaining Cubic Gate that the Denizen will use to bore through the Barrier. Various alternate paths here (at least deciding to go through a downed spacecraft that holds an Elder Evil is stasis or through a glowing fungus forest and play hide-and-seek with an albino Gug), and they end up at the edge of an underground sea. The Denizen is already at the city, which lies on an island out on the sea. Party goes out, stomps him and his summoned beast and realizes that they are too late and that the Barrier will fall in 1d4+1 years.

After that they players are tasked by the Queen to rally an army and stock up resources for the inevitable extraplanar invasion.

TL;DR The players start out as regular adventurers and realize that the rabbit hole that is the world goes far deeper than they thought and that the legends that they thought were just legends are indeed fact.

The end goal is for them to save the world from a fiendish invasion and either A) stay to protect the world and then ascend to diety status upon death, or B) launch a counter invasion of Hell. The lack of the planar barrier will also allow for Summoners to be a thing and the extraplanar influences to start to affect local politics and races.

[JusticeZero]

Right - if you want to surprise them, it is best to do so by introducing a formerly unknown element that the players have never heard of. Look into mythology of other countries for things that are downright odd. Slip them in in your game in places where they did not think anything was, even though they are not in the context of your game culture. Qalupalik or Kushtaka in your Mediterranian-ish setting, for instance. (Don't know what those are? Neither will your players, most likely.)
Then, and this is important, do not name them. Just give description. If the players nickname them, write that down as the name and use that name instead.

[illyrus]

Personally if we were playing D&D and the GM was swearing up and down that there were no monsters then I'd expect them even more. I think a simple "your characters have never seen a monster, they only ones who have get put away for being nuts; if they exist it all then they'd have to be pretty good at hiding" would do fine.

Personally I'd rather do the first reveal as more subtle then something like a werewolf attack (I realize it was just an example). Maybe some fey that masquerades as a human and knows some common vampire lore. The fey starts playing up the vampire tropes one by one and the party becomes more and more convinced that they have a vampire on their hands. When they finally splash it with holy water, present a holy symbol, turn it, try to drive a stake through its heart (thank goodness for fey DR) it screams in terror/pain that gives way to laughter.

If I was going to run it more straight then I'd modify a bunch of the weaknesses. Shapechangers have DR/obsidian, a troll-like thing looks human and only gains regeneration for a few rounds upon consuming the flesh of humanoids or by ripping off their limbs to replace its own, etc.

Stuff that within the game will make sense and the characters can research, but the players having foreknowledge on monsters will do them little good because the smart monsters will play at being something else or monsters are just different than presented in the MM.

[Alejandro]

That'd be like saying "you don't need to put points in swimming because the campaign takes place in rural colorado", then magically teleporting your party to oceanworld in the first session.

Depending on where and what season in Colorado, you'd be surprised. :) But I get your point.

[Water_Bear]

I like the idea that a seemingly mundane(-ish) world where the characters think they know what they're dealing with suddenly turns around on them, but this seems like the wrong way to do it.

Rather than manipulating the Players directly, which is going to piss them off and make them less likely to trust you in the future, you should control character knowledge.

Like, you might say "Learned people know that monsters only exist in fairy tales" instead of "This world has no monsters" in the beginning.
Or if they make a Knowledge (Monster Lore) check, say "You remember that the <Monster> is a fictional creature which in myths is said to <Monster Info>."
Or if a +1 Sword of Ogre Decapitation shows up and they identify it, say that it's a weapon which in legend was said to be able to cut the head off an ogre in one swoop.

That way the Player's don't feel dicked around, their abilities still work, and there are even rewards for players smart enough to read between the lines.