How to deal with player MacGyver-ism?

Question

Role playing is an excellent hobby to train your problem solving skills. You learn to look at situations from different view points (i.e. the characters) and you have various skills and resources at your hands (from dangerous to trivial, from magical to mundane...) which you will often sort through, combine and apply to solve the problem at hand.

In our group of RPG veterans this fact leads to a strong prevalence of what I will call MacGyver-ism. Let me explain using an example:

One of the recurring items is the molotov cocktail, or some genre-specific variant. It is highly efficient, trivial to create (pour liquid into bottle) and the ingredients are wide spread and cheap (gazoline/lamp oil, a bottle, some cloth). The process seems to be so simple that even untrained characters of low intelligence should easily be able to do it.

Just as MacGyver will do in his shows, the players will often combine mundane items and/or trivial skills in unforseeable ways to get an advantage, be it combat or plot wise. This can lead to solutions which are:

• very unrealistic given the setting (i.e. some medieval character would probably not know how to manufacture a molotov cocktail)
• overpowered (tips balance of certain encounters/problems, especially low-tech close-combat settings)
• are hard to forsee/prevent, as the needed ingredients are wide-spred and freely available (I can hardly keep my players from buying lamp oil or bottles)

So far I have not yet found a very compelling reason why my players should not be creating molotov cocktails (or similar improvised devices) all the time, and in settings where such solutions seems to be very unfitting (say, high fantasy).

How can I limit or control the prevalence of over-improvisation or MacGyver-ism in players actions?

As the first answers and comments heavily focused on the molotov: I am just as well concerned about players being true to their characters knowledge and possibilites as I am about the problem of power balance.

A medievalish soldier just should not possess the knowledge to build improvised firearms, bombs or complicated mechanical contraptions.

I have absolutely no problems with PCs being smart, creative and inventive while solving problems. I have a problem though, when the players are smart/inventive in ways which don't fit the setting or their supposed PC knowledge.

As it was suggested that his question is not entirely system agnostic (I somewhat agree), here some systems where I have struggled with this issue: MERP (low magic high fantasy), Call of Cthulhu (Investigative/Horror), DSA (high magic high fantasay)

Answer 1

The Molotov Issue

Don't punish or limit your players, Challenge them!

Your PCs may be great at coming up with incendiary devices that'll wreak havoc on their enemies, but once those enemies foolish enough to fall into the trap are dealt with, it stands to reason that the next foe will come prepared. Indeed, they might even pick up on the idea of using Molotovs themselves, which will create interesting challenges for the PCs.

Like @Joshua-Aslan-Smith said in his answers. The use of ingenious gadgets are bound to get the attention of noteworthy people: for good and for bad. Use this to provide new, exciting challenges for your PCs.

If you must limit, do it in-game and in-context

Word is likely so spread that the Molotov is highly efficient in combat. When it does, lamp oil will become a more treasured commodity, which should increase the price, perhaps the military buys all available lamp oil, thus making it less likely that the PCs can afford it willy-nilly. This could make for an interesting adventure: the PCs really want the lamp oil, allow them an attempt to steal it from the military.

Furthermore, carrying a bucket load of Molotov cocktails is not only uncomfortable and cumbersome, it's also highly dangerous. Imagine yourself walking around with a backpack full of gasoline-filled coke-bottles with little or less in ways of stoppers or the bottles breaking.

If your players do not carry a lot of Molotovs at once, I think that the problem will solve itself once they're in battle. Molotovs are, after all, one-shot devices.

General MacGyver-ism

Much of what I said above applies here as well (don't limit, challenge), but I'll spend a few lines expanding on this.

Having PCs that are creative and inventive with their playing is usually a very fun group to DM, even more when compared to the opposite. Allow their creativity and ingenuity to thrive: encourage them to seek new solutions and fun ways of doing things. You come off, to me at least, as a good enough DM to handle it.

It can, admittedly, at some point get out of hand (when the Dwarven Engineer in your low-fantasy setting starts talking about propelling slugs through a small, handheld pipe via controlled explosions, for instance), you might wanna step in. There are many ways for a DM to limit the PCs, both inside and outside the game. A few of them follows:

• Talk to your players. If they are veterans, they should be aware of the concept of metagaming, and how and why to avoid it.
• Carefully limit them, in-game. The things they want to buy is out-of-stock, they can't find the right merchant or similar. Your PCs may not be thrilled about this limitation, but if the level of limitation matches the level of outrageousness in their idea, they can't really complain.
• Simply tell them: this can't be done. A DM is within his or her rights to make such calls. It's not fun having to do it, but sometimes it's necessary. A brilliant example, in my opinion, of when a DM should have stepped in like this can be found in the Movie The Gamers: a thief uses pickpocket to steal a man's pants. While he is wearing them. While sitting down. A moment later, the thief constructs a ballista inside a tavern and backstabs an enemy with it. The scene can be found here.

Notes

The views I have expressed here are based upon twelve years of on-and-off tabletop roleplaying as well as being the DM for a handful of campaigns of varying game systems, length and, for lack of a better word, seriousness. I do not, by any means, claim that these are the only solutions, nor necessarily the best ones, but merely the ones I have tried and found to work well.

Answer 2

Historically speaking, your players aren't doing anything wrong.

Incendiary weaponry has a long history in Europe stretching back to the early middle ages and "dark" ages. Fire was and is a psychologically powerful weapon and all sorts of things from flaming oil to bursting clay pots were used against enemies. See Greek Fire as an example from as early as the 7th century.

Despite much romanticism about the middle ages warfare was, as it is now, a dirty business focused on killing and incapacitating as many of the enemy combatants as possible so to force political capitulation. Incendiary weapons were powerful tools to damage many enemies at once while also striking fear at the same time.

Balance shouldn't be an issue: Anything PCs can do, the GM can do better.

If their use of improvised incendiary weapons is such a key force multiplier that it literally trivializes combat, enemies and others in general would probably take note and deploy the same methods the PCs are using. Aside from fighting fire with fire, they might even come prepared with their clothes soaking wet and bags of sand to handle the fires caused by the PCs.

Don't punish your players for initiative and problem-solving; reward them.

The reward for a job well done is a tougher job. Their exploits and adventures should eventually reach a noble, maybe even the king, and their battlefield finesse and tactical acumen should eventually find them obligated/drafted by Authority into larger, more challenging events. OOC stifling player ideas and creativeness is a great way to destroy your game; resist the temptation to do so and go with the flow.

Answer 3

In a word Don't.

You have smart players that like to take advantage of putting together common things to solve unique problems. They have just made life for you very easy by showing you exactly what they want in a game.

My actionable advice is this; Design challenges without a solution. Not all of your challenges, but enough to sate your player's appetite for blonde mullets with duct tape. When you design these challenges, make sure your players have access to large amounts of common items and resources. Let them figure it out. It is what they want, anyways.

I would strongly recommend against artificially limiting player creativity. That would be an obstructionist style of game-mastering, and that, for me as a player, is not fun.

Additional Thoughts

If it is possible to succeed, something should happen

If your players come up with some Rube Goldberg machine of a solution to a problem, and they have not botched their rolls, and it is possible that their solution could work, no matter how implausible, there solution should change the state of the problem. It should do something.

If it is impossible to succeed, the characters should be able to figure it out

They came up with a solution, and it just won't work. It should be obvious, in character, that it will have a catastrophic outcome. Don't just proclaim that it does not work after your players put effort into these things.

Sometimes traditional problems have traditional solutions.

Don't nerf your characters, but if there is an encounter where the most logical solution is the traditional one, you should reward your players in doing that.

Take a poll

My advice up to this point has assumed that all your players are doing this, and they all get satisfaction from it, but it is possible that this is not the case.

Ask your players if this is actually what they want to do, or if they feel that the game is forcing it on them. If it is the latter, consider lowering your 'challenge rating' (use of a D&D term not withstanding). If they answer that they like, or most of them answer that they like the creative, non-traditional solutions, go full steam ahead in making that one of the center points of your game.

Make sure everyone is involved.

If this is the actions of one or two players, make sure you balance that with the traditional problem solving for your other players. Design some challenges that fit those players play style. If the Richard Dean Andersons at your table are the assertive types, engage the other players via an NPC to get their plans.

No such thing as Bad, Wrong, Fun.

If they are all having fun (see last two points), don't do anything. If they are not having fun, listen to your players, and address their concerns. I cannot give further advice on this, unless you have this conversation and post the outcome.

Your fun counts too

If you are not having fun making a campaign for a party of mulleted geniuses, let your players know. A toxic play table ruins everyone's fun. I do get from your frustration in your question that this is not what you had planned. However, I suggest that you try and make this part of your planning process. If making this kind of thing a center piece of your game is really killing your fun, then you have to stop and solve this with your players as people, not as players and gm.

Answer 4

The problems with your approach seems to be the problems with MacGyver:

People don't just instantly invent super technology that works extremely well and immediately solves problems and defeats strong opponents, except rarely and in extremely limited conditions that usually involve one-time surprises more than it's that their invention is a new uber-weapon. Like the makers of MacGyver, you seem to have a tendency to allow any inventive-seeming idea to be invented, designed, produced and deployed in a short time, and to work extremely well, overpowering conventional situations. That's over-representation of how easy, quick and effective invented technologies are.

Also, unless you and your players all agree and enjoy that you are playing a MacGyver game, you shouldn't be handling it like it is.

In the molotov cocktail case, you are thinking this sounds like a super-powerful weapon that has advantages over, say, a trained fighter using a sword, but it's not. As others have pointed out, many medieval games include rules for fire bombs, and they're not that great. Without gasoline, they are just auxiliary devices that can sometimes be useful or give an edge, but are clumsy to use and not that effective. Going into combat holding a lit torch and bottles of oil leaves you exposed and likely to be taken down and end up burning yourself, and lamp oil doesn't burn all that hot and will take a while to hurt someone in armor - even if you hit someone, they can finish the fight possibly without much injury and then roll on the ground to put the fire out.

In the case someone mentioned of a "dwarvish engineer" inventing a gun - read up on how many years (lifetimes) it took collective efforts of Europeans to develop useful and reliable firearms, and how bad the early versions were.

In other cases, these are usually clever tricks which will require not just the idea, but developing the idea, various uncommon materials, craftsmanship, trial and error, certain conditions, skill development, lots of uncertainty, lack of disturbance or discovery by opponents, surprise/panic/foolish reactions by victims, etc.

The GM is the one who gets to decide how effective any improvised course of action is.

So, learn historical and realistic perspective and apply it to your estimates of what it will take to realize an idea, and what the odds of success will be. Many ideas may work once, or almost work but instead waste lots of time and effort but not quite work, etc.

And of course, actual good ideas may be good ideas and deserve rewards and results and be fun... and if they are general purpose, may be copied or countered.

There is also the issue of player knowledge versus character knowledge and ability. Again like MacGyver, I suspect you are allowing the players' enthusiasm to translate into character abilities that aren't on their character sheets. MacGyver is a super-hero specialized in inventing ridiculous devices in a few seconds based on encyclopedic knowledge and super crafting skills. None of that, I suspect, is on your players' character record sheets. These things should be explained and agreed to up-front as part of explaining roleplaying expectations. One form is bringing players' 21st-Century knowledge into medieval fantasy worlds. Just as the player can't have their other-world character talk about USA pop music, they can't have them know about chemistry or anything that their character wouldn't know about from the character's own experience. If a player can't handle this, then they aren't capable of roleplaying from the setting, and need to either be restrained or to play a time/world-travelling character, if everyone agreed that would even be allowed. Now, if they actually want to play a plausible in-world character who is highly inventive and educated in rare-but-in-world knowledge, then they just need to use characters where that is appropriate in the game system, with the trade-offs that involves in the game system. I.e. they need to build their characters with the knowledge and brilliance they are going to want the character to have available, rather than allowing any PC to be brilliant while playing a combat-optimized barbarian with no in-game specialization in such things.

You mentioned that you "can hardly keep my players from buying lamp oil or bottles", which is true, but you can require them to have some in-world, in-character information or Galileo-like invention talent which allows them to get the idea to do something, or for the PC's to invent a new idea that the characters don't have.

You might also want to try having the players try to do some things in real life that they think they know about, but have never done, to give you all some experience in what real-world MacGyverism is like. Try having non-cooks try to cook a soufflé or other semi-difficult recipe and experience trying to get it to turn out right. Try to attach a tablet connected to video conferencing software to a radio-controlled helicopter which lacks a camera, and try using it to guide its flight in first-person. Try having a guy with a water balloon try to defeat someone with a Nerf bow-and-arrow or Nerf sword. Try building a catapult. Etc. See how many hours or days and failures it takes. Imagine having to design and build things with no access to modern tools or shops. Etc.

Answer 5

Are We Overthinking This One?

This is a classic game balance situation. On the one hand, no DM ever wants to hear themselves say, “stop playing so good” or “in the middle ages everybody was dumb.” On the other hand, player improvisations can get, well, out of hand.

Believe it or not, there is a really easy fix for things like this. It’s not in the rule books and it doesn’t require altering your campaign world’s military or socioeconomic realities.

Just think of these two words - MURPHY’S LAW - if something can go wrong, it probably will.

MacGyver gadgets and other Rube Goldberg devices, cobbled together from twigs and rags are notably unreliable and unpredictable weapons (swords on the other hand are quite predictable). The more dangerous such a weapon is for one’s enemies, the more dangerous it will be to the player who carries it around.

Consider the X factor in a medieval setting, where there are no manufacturing standards. No two ceramic jugs are the same. Ale and mead don’t have labels guaranteeing their alcohol percentages. Flint and tinder can’t reliably pull off a flame in seconds. And combat environments are not sports arenas offering consistent battlefield conditions.

Brainstorm of ways for MURPHY’S LAW to stop a medieval molotov cocktail.

• Bottle breaks too hard - it hits the opponent or ground and fails to break, but it’s still on fire so you better stand back.
• Bottle breaks too easy - player is struck in combat setting off one of their MacGyver bombs. BOOM!
• Can’t get it lit - round after round and the player just can’t get that fire going. Particularly interesting when monsters are trying to eat you.
• Burns too fast - goes off in the air on the way to the target or in the player’s hand.
• Burns too slow - hits opponent and bounces off. Later when the PC's are searching the bodies for treasure, BOOM!
• Dangerous environment - burning oil hits some leaves and soon the whole forest is burning or smoke draws more enemies.
• Difficult environment - it's raining, enough said.
• Unpredictable enemies - burning opponent decides to charge PC’s and take them with him.
• And most realistic of all - it hits the opponent and most of the oil just flops to the ground and the opponent steps out of the fire taking minor damage.

I think what happens in situations like this is that the players think like modern people and try to create a modern weapon - when in fact they created a medieval weapon. The DM fails to realize this and in their mind substitutes medieval molotov cocktail for modern hand grenade, allowing the contraption to be far too effective. If the DM imposes some murphy’s law and common sense on the player’s initiative and the players still manage to make it effective, then they deserve all the credit. But good luck making things like this work all the time.

Answer 6

Technically, @Joshua Aslan Smith 's points are correct, and in general they're good maxims for a GM to follow. However, @BESW 's comment on the dangers of escalation of brutally effective battlefield tactics is spot on. Even for more mundane applications, occasionally someone comes up with something unbalancingly clever, and while you definitely want to reward the player who came up with it, you have to reserve the right to curtail it's use if it interferes with the game, by limiting your ability to keep it fun and challenging or by taking the narrative in a direction that makes you uncomfortable.

I, for one, am not a big fan of unilateral metagaming limits in my games. (Translation: I hate saying, "You can't play that way even though it's technically possible because it breaks my world.") If I do, then I feel like I've failed as a GM. Unfortunately, the only other mechanism I've found to deal with these issues is to just be really, really clever, or at the very least, uncharacteristically thorough.

If some technique is unbalancingly effective, then you should be able to reason through a rebalancing change in your world to adjust for it. For example:

1. Materials that support it become prohibitively difficult to obtain in large quantities. Or just prohibited, as the local constabulatory fears it will be used against them. In the case of burning oil, highly combustable oils go in short supply -> domestic use switches to a less volatile solution that doesn't have it's pricing affected by military uses -> tactically useful fuels become expensive, or governmentally regulated, or even outlawed for private use and relegated to the black market. They can still get it, but only small amounts.

2. Look for rational reasons why it hasn't already been tried. Do your heroes really think they're the first ones to come up with this? Often you can craft reasons or chains of cause-and-effect explaining why it's use is limited. Again, picking on oil, fires in underground complexes burn up oxygen, produce deadly smoke, and in some types of construction weaken the intergity and cause collapses. Fires in the open can start wildfires that invariably end in very pissed off farmers and villagers, or are mistaken for "mating flares" by horny red dragons. And let's face it, there really is no good way to cheaply and efficiently transport large quantities of highly volatile material without risking a nasty surprise. Entire economies pop up around that sort of thing.

Bottom line, powerfully effective techniques get noticed. Also, a good world setting is a highly adaptive organism. Take the time to walk through how your world would evolve in the face of your players clever discovery.

One additional note: If your players feel you're abusing your power just to limit them, make them famous/infamous in your world for their idea. Name things after them. Give them a widely-known reputation for cleverness, or ruthlessness, or luck, and then use that reputation as the basis for plot hooks. Players live for moments like overhearing a bar conversation about how badass they are, or having an official proclamation distributed across the kingdom asking for their (oh so clever) help with a national crisis.

Answer 7

I have absolutely no problems with PCs being smart, creative and inventive while solving problems. I have a problem though, when the players are smart/inventive in ways which don't fit the setting or their supposed PC knowledge.

It seems to me that this is not an in-game issue, it is a social contract issue. The same could be said if the players were not showing respect as samurai to their lord, or using modern sensibility in any historical game, or using out of character knowledge as if it were in-character. As such, it is best dealt with in an assertive manner, out of game.

I would approach it as: "Gales and guys, I noticed that you keep using modern technology/knowledge to solve things. Why is that?" If nothing happens, ask: "Are you feeling that the setting appropriate methods would not work? Why are you falling back on modern thinking? Do you see my role as a GM as the adversary you have to beat? ..."

If the players really want to be exceptional inventors, that's great! They can making theories, then experimenting, and finally getting something new and wonderful. This opens up a great side plot line. For example, in a medieval setting, they invent gun powder and guns. Now, warfare will change, the balance of power is tipped, and nothing will ever be the same. This would be a great game to play in!

Answer 8

Most "gadgets" are surprisingly difficult to get right. I know you don't want to focus too much on the Molotov, but it's actually a very good example on how to challenge the feasability of the gadget invented.

---

Molotov: Put flamable liquid into bottle, stick wick to it, light wick, toss bottle. Sounds easy, does it?

1. Getting the right container. It's easy to break a wine bottle on a tank, but you will have a really hard time to break it on more "medieval" targets like a person, foliage, etc. unless the bottle is made of extra thin, fragile glass... which makes transporting it in your backpack interesting. Besides, glass containers of that kind of fragility tend to be really expensive in a world of pottery tankards and leather wineskins...

2. Getting the right liqiud. Your standard issue lamp oil simply doesn't cut it (because of a much too-high flash point, it needs a wick to actually burn), you need something more volatile than that. And while gasoline, high-percentage ethyl alcohol etc. might be easily available in our world, good luck getting such highly-refined products in a medieval world for any reasonable price.

3. How do you light the wick, again? Flint and steel? OK, takes a minute or two. Fire spell? OK Mr. Spellcaster, stop casting combat spells for a round or two to light my Molotov, why don't you?

4. What's your "thrown weapons" skill, "bottle" specialization? Make your skill roll. Ah, not quite... Rolemaster, for example, has nice "scatter" rules in one of its Companions. Tossing a Molotov into a melee gives the term "friendly fire" a whole new meaning...

5. How did your character get the idea in the first place? I mean, sure, the player has seen it in the movies, but unless a Molotov is a common item in the game world already, I'd expect some good rolls on whatever "Tinker", "Inventor" or "Engineer" skills the character has which might be appropriate given the game system and gadget in question.

And don't give me that line of "I'll just roll until I invent a Molotov", that's not the way it works (at least where I am the GM). Your character has to face a real game-world problem, sit down and think it over, and then roll to invent something (decided by GM), not something specific (decided by the player).

And if he's a smart character, he'll probably ask himself, "how long will it take my enemies to copy my invention?" The answer to that could well be, "not long enough -- better shelf this and hope they don't have inventors as smart as myself".

---

This was only about the Molotov, but similar ideas borrowing from this-world experience would face similar problems. Thinking about a contraption is easy. But even something as "simple" as a snare can be surprisingly difficult if you sit down and actually try to build one.

---

The most important thing I make clear when assembling a new group: Earth science does not apply. Even if the world has things called "coal" (black burning stone), "nitre" (salt used for curing) and "sulphur" (yellow stuff used e.g. in bleaching), mixing them will most likely not give something that goes "BOOM!". Rubbing "amber" (nice brown stones used in jewelry) on certain cloths does not yield electricity, and forget about building a generator with a mill, a length of copper cable and some magnets. Chemistry, Biology, Physics, forget it.

Does. Not. Work. (Or, at least, not as you learned it in this world.)

---

Ask the player to have his character come up with something, not the player giving the character some ad-hoc epiphany wildly out-of-touch with what the character knows, has ever seen, or could possibly envision.

Answer 9

In some game systems, you can remind them that they are playing a character, not themselves.

Have them roll against their intelligence, idea, luck, education, wisdom, etc to discover if their character is capable of coming up with the idea, then against other attributes to find out if they actually carried it out successfully. You don't need to make it impossible, just make it so they remember, "Oh yeah, I'm playing a character."

Add some levity and they'll probably accept the criticism well.

"Unfortunately [character name] neglected their studies in the parallel-universe 18th century medieval England technology class, and must roll against their farsight ability to come up with that idea."

By user their character's name and moving to the third person you force a gentle shift in perspective. Go back to "you" immediately after so they can re-immerse. This shouldn't result in an argument or meta discussion, just a quick tap on the shoulder and reminder.

Answer 10

The other posts have great comments about in-game and meta-game ways to limit this. I'd like to address another reason why MacGyvering may not work, namely that MacGyver had a team of writers inventing the scenes and a team of prop-makers and set-builders making the scenes work.

Things that look easy on film are not necessarily easy in reality.

For example, check out the molotov-throwing failures in this video. In fact, a recurring theme in Cracked.com's articles is how we as a society are seeing things on screen and trying (and failing) to emulate them in reality.

On the other hand, a roleplaying game is also fiction, and we play games to have our characters do cool stuff like in the movies. :-)

As an aside, in a medieval world, glass is hard to shape and thus expensive, especially if you want flasks that break on contact with the target but don't break in a backpack. Economy will certainly affect the ability to buy them. "You want more flasks? What did you do with the last lot?! Anyway, come back next week when I've finished making more."

Answer 11

Why so stressed about the molotovs?

I'm not familiar with the setting(s) in which you're GMing these games, but I know that even regular old D&D provides explicit rules and damage for throwing a burning pot of oil. It certainly isn't anything game-breaking. I also don't know what the circumstances of these characters crafting these molotovs are, but it seems to me like you aren't making them roll for it. Burning pitch was the most common incendiary weapon in the medieval era. "Pitch" is a catch-all name for a concoction of natural or manufactured substances designed to be flammable and burn hot. This means that anyone trying to mix pitch would have to have at least some working knowledge of chemistry and possibly biology. Under most fantasy systems, this skill would be called "alchemy." Gasoline and styrofoam do not exist, and neither does the internet, in most fantasy settings. You are the GM after all, yet your post suggests you are somehow powerless to stop your players from oppressing you with firebombs.

This can be applied to any issue involving metagaming. All you need to do is calmly explain to the players why their characters don't know how to do what they're proposing.

By the way, I don't mean this as a slight, but crafting a molotov is hardly the most inventive and creative thing I've ever heard, especially if it's being done repeatedly. You seem to be predisposed to reward it just because the players figured out how to do something that wasn't explicitly in the rulebook. Suicide melta-bombing a hivemind of worms that is immune to normal damage is a pretty decent and creative way to deal with a xeno far ahead of when the GM expects, using Dark Heresy as an example. That cleric had to burn a Fate.

Answer 12

I'll try to cover some ground that hasn't already been well-trodden.

There are two things you should keep in mind about the characters that will make for a more immersive game:

1. They are almost certainly not the most powerful group of people in the game, and
2. PCs do not exist in a vacuum. (Unless you're playing a space game, but I digress...)

One of the things that keeps a long-term game more interesting, even in the face of a whole host of challenges like MacGyverism, is that when the PCs push the world, the world should push back. In terms of my above points, consider that in any game world there are going to be various groups who are very deeply interested in maintaining the status quo (or some specific parts of it) and who will be interested in the inventive PCs either to gain their knowledge/assistance, or to quash same. Some of these people will try persuasion, some will try brute force, and yet others a mix of the two.

Consider, for instance, that one or more "gods" may not want any kind of serious technological advancement to occur, for some reason(s). PCs who threaten to break the mix of what is and isn't allowed might incur the displeasure...or even the outright wrath...of said deities and their churches, some of whom might be less than kind in their attempts to dissuade such activities.

It doesn't even have to be divine wrath; perhaps the aristocracy is worried that such things could upset the balance of power unfavorably. The PCs might suddenly become popular in ways they don't enjoy. (Consider, for instance, all the work that has gone into learning and protecting the secrets of nuclear technology from WW2 to today. The same sorts of push-pull could happen to our happy inventors.)

One other way that the world can push back is in its mechanics. Perhaps technology and magic mix like sodium and water...or perhaps high concentrations of one keep the other from functioning well. If there are mages in such a world, they might be very interested in preventing tech development because it presents a threat not just to their livelihoods, but their lives.

Whatever you choose, just think it through and have your logic set so that the players can see that it's more than just GM fiat at work...then let them have fun, keeping in mind all the other wonderful guidelines others have presented here.

Answer 13

You've put your finger on one aspect: MacGyver, and television in general. Players used to such shows (the A-Team is another classic example) are thinking in that frame. In essence, they're playing one genre - comic adventure drama - and you're trying to run some other one, depending on the game.

I've seen untrained people try to use molotovs and set themselves on fire; I know of a case where someone burnt their own house down simply trying to prepare a batch of MCs for later use. That's a clue to the solution - real life is not like television, and your CoC game doesn't have to be either. You need to signal this to the players by asking two questions/setting two tasks.

The first one is "Does the character know that?" E.g., does the character know that tracer bullets might ignite hydrogen in a Zeppelin's gas bags; do they know how tracer bullets work? In D&D terms, that for me is a Wisdom roll. In CoC and other games there may be a knowledge skill or similar which could be applied.

But it's not a one-step problem. Tracer bullets on their own are very unlikely to work in their standard configuration. Does the character know that they'll need to fire only tracer bullets to have any chance of success? That's another test. In other examples there may be many tests - even the molotov is a combination of fragile container, slow burning wick and combustible liquid. Don't let the player railroad you into treating it as a single invention and a single roll.

The next step is combining the parts - the second question: "Can the PC actually manage to make this thing?". To me, that's broadly an Int roll or maybe even an "invention" test if the system has such a thing; again, it may be more than one roll or maybe modifiers to a single roll based on complexity.

In the case of the tracer bullets, it may be a more practical mechanics or Dex test to adjudicate whether the PC can scavenge tracers from multiple belts and feed them into a single belt to produce a concentrated effect. A fail may not be obvious to the PC - the gun might jam when fired later; if it's a really bad roll, perhaps the tracers in the belt are set off by an ignited bullet that is jammed. Hilarity ensues.

Finally, of course, the idea might not work at all. This Zeppelin is held up by magic or helium or invisible swans. Or the idea simply has a chance of working and the PC gets unlucky. Sometimes players can react badly to not being told why their clever idea didn't work (and sometimes even if they are told). You can hint to them by saying "Things are not as they appear" or whatever, but resist out of game explanations. Let the player investigate their failure in-game. Then, if they come up with a better plan later it will be the result of in-game development instead of player/character knowledge leaking.

One big justification for player ideas failing is technology, and the two big ones here are precision and materials. No matter who you are, the internal combustion engine is not an option in 1200's England. The materials available are too brittle and heavy and the machining needed to make small gaps that don't jam when the heat changes simply isn't there yet. Refined fuel is also a problem, as it is for the molotov. Even 1920's America has a lot of limitations, especially when out in the field. Middle Earth mostly seems primitive compared to even to the mediaeval period and most clever ideas will require an elvin smith or similar exceptional characters and equipment to attempt; magic is probably the easier option, especially in MERP where magic is really too easy compared to the books IMO.

But sometimes you just have to say "no". If you're playing classic Traveller, hyper-jumps take a week and there's nothing the players can do about it ever. There's an entire empire of scientists out there that haven't managed to do anything about it, so your PC ain't going to change it and the same goes for many other things.

Similarly, a phylactery is something you wear. That's all there is to it. A lich PC can't leave it somewhere safe and have the advantage of it any more than s/he can leave a +3 ring of protection somewhere and have the advantage of that. If the player has played in a system whose author didn't know what a phylactery was then you have to just say "no, that's wrong" if they try the safe-keeping trick - sometimes player ignorance can leak over just as much as player knowledge.

So, some things are campaign-givens and no amount of invention by players can get around them. It's the GM's responsibility to present them in a way that makes it clear why it is that way, or to change it if they can't. Computers in Traveller were a good example of this - they were wildly under-powered even by 1970's standards. GMs either re-wrote the rules completely (which was hard to do and keep the balance) or invented weird scenarios about semi-conductor eating yeast or alternative histories of analogue computing to justify the rules as written.

Answer 14

If you aren't a strict simulationist, you can also have things only work the first time or when narratively convenient. Prepare this by already explaining the first time why it might not work.

For example, in the case of Molotov cocktail, a simple reason it may not work is that not all flammable liquids explode. Alcohol needs to be ~40 ABV to even burn and distilleries weren't necessarily that accurate or distributors so scrupulous that every bottle of whisky goes that high. Oil burns, but doesn't necessarily explode, depending on purity and density, among other things.

So the first time you can say that you roll to see what happens, but have it succeed with 100% chance. If they try it again, you can roll against as small a chance as you like.

Depending on your players' preferences you may do this openly, letting them know that innovation is good, but that they won't be able to reuse tricks infinitely. Or you can hide it from the players and let them figure it was luck the first time.

Answer 15

I had the same issue few times, and I couldn't solve it much better than you - once the PC's invention became known, a lord sent assassins to kill the PC and prevent spearind of air guns, which could one day endanger armored knights and thus break the dominance of chivalry (just like crossbows were forbidden for a long time in Middle Ages). Now, years later, I think I see better solution.

This is basically a social contract issue. You expect high fantasy, they expect "clever men's game". "Breaking your world" is no problem in a generic oldschool sandbox where you are expected to react on the players and give them some challenge - others responded well on what to do in this situation. But it is far away from the feeling most of us expect from playing in Middle Earth. If the players don't appreciate the high fantasy feeling and take Middle Earth as any other fantasy with the bonus of opportunities of outsmarting Gandalf, then a molotov cocktail seems logical. The problem is when some players want to enjoy a high fantasy heroic saga (seems that you do) and others want to outsmart the GM and don't care of the genre.

The solution is to sit with the players before the game, explain what you expect and then either agree that you play high fantasy and MacGyverism must be limited to the genre's scope, or that you play oldschool and any good idea is OK even if it seems odd in a fantasy setting. The key is to find out what each player likes and finding a compromise so that every player is satisfied.

If the game is already running, it may also help to explain each player's motivation, but you can't blame a player expecting a challenge where winning is the highest goal for playing in the style he expected, even though you thought of it as of an epic tale of chivalry and honor, where roleplaying and keeping genre is more important than winning.

Probably the "MacGyvers" enjoy outsmarting the "enemies" and expect a style where they are not constrained in their "clever ideas". But this might just be the only style (or one of the few styles) they already know and they would gladly try something new. Perhaps they would accept a challenge of being constrained by the genre - if they started the game with explicit agreement that this is important part of the game and knew that other players prefer genre-pure story to winning combats due to Molotov cocktails. I don't know your players, but many players, even "experienced" ones (in one style) think that the point of the game is a duel of wits between them and the GM, or even that loot and XP is enough for a good game. Many of such players can quickly start liking more "roleplaying-oriented" style, if someone presents them the style in the right way. Talk to them and try to explain that roleplaying could be more fun than hack'n'slash or oldschool winning. Inviting someone experienced in story-oriented style to host a one-shot might be a good way to show what is possible and what is fun.

It is still quite possible that most players will agree that they don't want to experiment with anything that would inhibit their MacGyverism - then you know that you can't play high fantasy with them if genre purity is important for you. Still, it's better than constant arguments whether MacGyverism is OK or not.

Answer 16

Man, MacGuyver had it easy.

Focusing first on improvised weapons like the Molotov (but not exclusive to it), how effective do they expect an improvised weapon to be, exactly? Sure, if they in fact have the talent to create it (with whatever weapon-crafting technique they want to use in the system you're using) they can give it a try, but it's not something just anyone can do.

Misfire Chance

Let's assume they are trying to create a Molotov. Are they making these ahead of time? Then there's the issue that if they fail, they're spilling and wasting oil (possibly soaking their clothes in it, NOT good), breaking a few bottles in the process, and then having to find a way to store them all comfortably for later use (and not in a way that lets that highly-flammable oil slosh around in their pack and turn them into an incendiary bomb). And this assumes they do it right, which they won't know until they use it.

And let's assume they do use it. As a makeshift weapon, in any system, it should have a high chance of failure or even misfire. Didn't stuff the cloth in tight enough? Now you're bathed in oil. Didn't stuff the cloth in tight enough and botched your throw? Now you're bathed in oil and on fire. This isn't exclusive to the Molotov either - any weapon they self-make out of makeshift objects should have a chance at failure

Skilled Craftsman

Granted, if they make an honest attempt and are really good at making real weapons, they should be rewarded with scarily and cheaply-made effective weapons. Don't punish your players if they decide to go down that route (though if you really don't want them to go down that route, make sure you address it before character creation is over).

---

Summary

But don't let just anyone get away with it either. Makeshift ladders made out of broken 10 foot poles? Guess how sturdy that is going to be (not at all). Thrown-together laser guns with paper clips, broken mirrors, and gum? Probably about a 50% chance it will explode or fire in the wrong direction.

On the other hand, a relatively simple incendiary weapon used by mobs for centuries that a trained military man has crafted carefully in his spare time? Perfectly reasonable.

Answer 17

Perhaps molotovs weren't the best example, because liqour and the fact that it's flamable is just a microcosm of pouring hot oil onto enemies at the gate then lighting it. Historically, it should be fine.

However, if your party is making a rapid firing balista out of some mundane items they found just lying around, then I think you can make it as difficult as you want through a series of rolls during construction. It doesn't take inventiveness and imagination away all together, but at least there's a larger chance that they fail outright and then they won't effect every encounter. Them failing will seem realistic, because no matter how high an intelligence score your wizard might have, it doesn't make him a mechanical engineer.

The DC Gauntlet

So you make the person with the idea roll an intelligence check to see if they can come up with the design for a complex mechanism. Int vs a DC difficulty you think would be realistic for what they are looking to create. If you feel like your players don't trust you because you keep making them fail when they try to create a nuclear bomb, then just tell them the DC when they roll.

Once that happens, make them roll again to see if they can find the proper materials in the area, again look at what they are building, look at the area and think of what materials might be around and make them roll a perception check or something like that vs. a DC that has a difficulty adjusted for the environment and whether it's logical for them to find the items.

Then once they find the items make them roll a final roll to see if they successfully assemble it all. This roll could be up to you depending on what the item is. I would make this roll the most reasonable considering if they've gotten to this point then in respect of the RP going on, the characters technically know exactly what they are doing. They've successfully got a design in mind, found the proper materials, this should prove they are well-versed in the task at hand. Make the roll moderate.

Bam, you've made them go through a moderately logical gauntlet of rolls.

You Control The Effect

Now, I'm not saying you should make them do this for everything. Honestly, let them make the molitovs without jumping through hoops, something that simple shouldn't be a problem for you. Instead for something like that, just do a couple hidden rolls; one for how many they can make, a roll of a d10 or something, you decide for balance. Then when they use them roll a check to see if they work or not. Liqour would be inconsistent in the time period, as many have said here, so it would make sense if a few of these were duds. If you're allowing something as simple as a bottle of liquor and a flame to derail your encounters then you as the GM are giving it too much power.

If a bottle of booze and a fire source are killing your encounters then you are either making the encounters to easy or more likely the molotov way too powerful. You are the GM, you get to decide this sort of thing. Take advantage of the power you wield.

---

Side Note: Please don't ask your players to make real-life molotovs to prove a point; that's dangerous.

Answer 18

Don't tell the players they can or can't do something. Instead, get them to justify their actions. If the person playing the idiotic warrior is trying to make molotovs, then ask them how their character learned that information. If they can justify it in a way that satisfies you as a GM, then fine, go with it. If they can't, then just say 'Sorry, but I'm not going to allow that.'

Answer 19

You seriously think that a medieval character wouldn't think of filling a clay flask with lamp oil, putting a rag wick also soaked in oil into the flask, lighting it, and throwing it? That's all a molotov is - and just takes some basic common sense. In this specific case the PCs understanding of what they can do is IMO more realistic than yours.

So how do you restrict molotovs? Simple. A molotov should never be as deadly as an arrow or a thrown dagger. If you want to kill someone use a sharp and pointy piece of metal designed for the purpose. The molotov instead should have two effects - the first being to set the ground on fire, and the second being to get the target to stop, drop, and roll.

There's no general case for restricting PC invention - it has to be done case by case. (No making gunpowder for example).

Answer 20

Trivial to create?

Ingredients needed:

1. A rag - easy to acquire.
2. A bottle - will be extremely difficult to get. Glass bottles were uncommon in England until 1845. Other countries may be a bit earlier, but if you're talking fantasy, then glass bottles will be a rarity. In D&D 3.5, a tankard costs 3 copper pieces, and a wine bottle costs 200. A local pub will serve wine in tankards.
3. High % alcohol - Also difficult. Historically, vodka was 14% ABV in the 900s, 24% in 1400s and 35% by the 1800s. Not going to be flammable enough.

In Call of Cthulu, this is not applicable, of course.

Answer 21

Part of the problem is that the game's carrying/encumbrance system does not adequately cover the difficulty of carrying gallons of flammable oil around with you ahead of time, as well as breakable bottles, and a source of fire, in order to repeatedly create and use molotov cocktails on demand.

Which is to say, molotov cocktails aren't the problem. Being able to carry 40 "oil potions" in the first place is the problem.

Answer 22

My tip: Make it hard to do in the middle of combat.

Player's initiative declaration: "I'm going to make a molotov cocktail!"
DM: What skill are you using for that? ... Do you have something that directly relates to making your molotov?
Player: Uh... not really... uh... he is a gnome inventor so I think he can figure it out...
DM: ok then... Roll a dex check at −5 ...Passes roll maginally... Ok you have managed to get oil into the bottle and all over yourself. Light carefully.... Flint and steel takes another round to use.
Monster attacks player... misses... you manage to defend yourself but roll another dex check at −8 ..fails.. the slippery and hastily made molotov slips out of your hand. whoops!

If it is really annoying make it something hard to do and add some skill/proficiency checks to it! GIVE OUT MINUSES TO THEIR ROLL! ... if this is something they want their character to be good at, make them use skills/feats/proficiencies for it. Dealing with oil is slippery and messy! If they are carrying around 10 bottles of flammable oil and a monster hits them... roll to see if any break. If they forget that they have splattered oil all over themselves when they light up, make it really bad. Nothing like a −6 to your charisma for burning off your face and fingers!

This kind of thing works for all types of improvised inventions... Especially if the character really doesn't know how to make what they dreamt up skill-/stat-wise. Don't say no! Tell them they CAN do it, but since they only saw it in a movie once/saw it happen at a tavern they may have trouble doing what they are envisioning. Make it hard to do. Especially if they're trying it in combat.