"I invent Greek Fire!" and other PC shenanigans

[Bae'zel]

My friends call this the "Greek Fire" phenomenon, based on a close friend of mine who likes to test the limits and confidence of new GMs. Especially when the GM is clearly high and/or drunk. Basically explains to the GM that they're inventing elaborate technology or tactics beyond the setting's time period to see if they'll let them get away with it.

So on that note, how do you gracefully handle players leveraging their historical and practical knowledge to have their characters build and essentially invent things in the campaign setting?

Time travellers, like Ash in Army of Darkness? Of course! A very clever Bronze Age soldier coming up with flammable grenades that get worse with water? Ummmm

Let's assume for a moment that the "rule of cool" has SOME limits (ie, during session zero, the players all agreed to run the campaign setting as genuinely and honestly as possible). What would be the best way to handle this without causing a fuss at the table?

What's the best way beyond just "NO."?

EDIT

One of my favourite responses so far:

Post in thread '"I invent Greek Fire!" and other PC shenanigans'

Jun 25, 2026

So on that note, how do you gracefully handle players leveraging their historical and practical knowledge to have their characters build and essentially invent things in the campaign setting?

I would treat it as a long-term objective, not considerably different than if the player wanted the character to create the next legendary artifact. It sounds like a significant amount of work and time investment to assume the power and experience to create/invent, say, the portable hole, let alone the Deck of Many Things --- so sure, have at it, but we need to talk about your steps to...

• bsss

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[Cordwainer Fish]

Rule -5: No ironworking tools on the playground. Yes, in the real world FTL would break causality; your character will not, however, attempt to bootstrap jump drive into time travel.

 

[VashVet]

I have found a feasible answer is to let their idea work but have only average effectiveness, making it no better than an average spell or attack - whatever is appropriate for the circumstances. Ultimately, the player is attempting to find an outsized result that exceeds what their current abilities grant them. I like to flip this around and focus on the idea and its success: is it more important to the player to have their idea work, but not be incredibly powerful, or are they just interested in the impact? If it’s the latter, then these shenanigans tend to take care of themselves when they find their pet idea is no better or worse than casting a 1st level spell, for instance.

But in reality, No is also a good answer, despite the question. Why? Because even in the question’s setup, it’s clear the action is not being done in good faith. It is being done to test limits of people. That’s simply not a great thing. I’d rather put up the fuss once and nip that kind of stuff in the bud then play out the interpersonal dynamic “game within a game” that is being attempted.

 

[Bagpuss]

I mean wasn't "Greek Fire" used by the Byzantine Empire in like the 7th Century I'm not sure which settings time period it would be beyond in that case.

I think the infamous "Guns, guns, guns" supplement worked on the principle that in theory the technology to build an SMG existed in the Roman era. The issues are the blackpowder back then would be no where near as effective as the charge used in bullets now, and the precision engineering would more likely need skilled craftsmen than machines so mass manufacturing and reliability would be major problems.

In principle I don't have a problem with people inventing things, just modern technology depends on so many previous advancements it's not like they could build an M1 Abrams over night.

Also in a lot of fantasy works technology is suppressed because it is just much easier and quicker to solve the problem with magic.

 

[Whisper-Kitten]

My friends call this the "Greek Fire" phenomenon, based on a close friend of mine who likes to test the limits and confidence of new GMs. Especially when the GM is clearly high and/or drunk. Basically explains to the GM that they're inventing elaborate technology or tactics beyond the setting's time period to see if they'll let them get away with it.

So on that note, how do you gracefully handle players leveraging their historical and practical knowledge to have their characters build and essentially invent things in the campaign setting?

Time travellers, like Ash in Army of Darkness? Of course! A very clever Bronze Age soldier coming up with flammable grenades that get worse with water? Ummmm

Let's assume for a moment that the "rule of cool" has SOME limits (ie, during session zero, the players all agreed to run the campaign setting as genuinely and honestly as possible). What would be the best way to handle this without causing a fuss at the table?

What's the best way beyond just "NO."?

"The materials you need to construct that are availiable some place in the world, if you can find them."

 

[Willie the Duck]

There are plenty of reasonable solutions:

• "Describe every step you take in this process."
• "You are successful. It does 1d6 damage per use."
• "You are successful. you now have a technology optimal for burning wooden structures in a siege situation (not dungeon-crawling)."
• "You are successful. It is devastatingly effective... and very expensive."
• "Your character doesn't magically know how to do things no one around them do. I see you have zero levels in 'world-changing inventor' class."
• "Chemistry works differently in this world."
• "The god of creativity comes confiscates it."

Added later:

• "Your character can make Greek Fire/Gunpowder. To be able to source it, experiment with it until they make a working weapon out of it, build the supply chain to produce in in quantity, leverage it into a world-changing invention, use it to conquer enemies, and avoid being assassinated/becoming some world leader's catspaw, they are going to have to master logistics, economics, politics, and strategy. That's a life's work, and not one particularly interesting to the rest of the party. We're instead going to follow the rest of the party's exploits. If you'd like to roll up a character to play in that game, you can play too."
• using gunpowder as example instead of Greek Fire. "You have control over your character's thoughts, emotions, and actions. However, your character can't just choose to invent some great world-changing invention. If that were something one could do, I'd be a bazillionaire. So, you can decide that your character is going to put together sulfur, charcoal, and saltpeter; but you don't know that that is the recipe for gunpowder in this world, and since you are actively trying an end-run around the verisimilitude of the inventing process, I am going to rule that it is not."

 

[Umbran]

"The materials you need to construct that are availiable some place in the world, if you can find them."

"The invention you are suggesting was not the work of one person, but of several people over years, building on one another's discoveries. You have not established that you have the work of others to base your invention upon."

"Note that this is a very dangerous substance, and it is possible, even likely, that an early version of it might ignite prematurely as you attempt to develop it. Are you sure you want to risk death by fire to create this invention?"

 

[Bae'zel]

I mean wasn't "Greek Fire" used by the Byzantine Empire in like the 7th Century I'm not sure which settings time period it would be beyond in that case.

I didn't know that; my friend insisted that ancient greeks used it so I guess they were wrong.

 

[dragoner]

You have like little Dromon flame thrower ships.

Anyways, yeah, I am open to being convinced, and with that knowledge, I might also say no. I remember the ultimate argument as kids, is that beer has alcohol, so the cheap beer in the AD&D DMG would burn. It was like no, beer does not burn.

 

[Bagpuss]

I didn't know that; my friend insisted that ancient Greeks used it so I guess they were wrong.

Well its that part of the world. I think the point is it isn't a modern invention in fact the secret was so well guarded that that real recipe is lost to time, but there is a general agreement on what some of the chemical agents were likely to have been.

Chemical inventions are probably the most likely to be able to pull off in a fantasy setting since chemical distillation is pretty ancient science. Levers, pulleys and the like should also not be too hard, but I don't think players are about to go about and invent the microchip.