Game System Hacking 101 pt. 2

 This article was originally published in Welcome to the Deathtrap, on Feb. 9th, 2021. 

Image by FunkyFocus from Pixabay

This is part of my series on tweaking and modifying the rules of a TTRPG, or stealing and hacking in the rules of a another TTRPG into the one you want to play, in order to let you build the experience that you want. In the previous article I discussed why you might want to modify a system, how to create a rubric to determine what is a desirable mod, and how to figure out where the system can be made to better suit your aims. 

In this article I am going to show you how to get your hands dirty and actually alter rules in a smart, methodical way.  To do this, you should have a working understanding of the rule system you are using. And have an idea of how it plays. 

What Should I Hack?

Assessing Rules

If you have done the first few steps, you should have an idea of where your system of choice doesn't quite support your desired experience. Knowing roughly where the problem areas are is the key to choosing what to hack. The next step is to have a look at specific rules and looking at which ones could be changed to build a better experience.

For example, I decided, when planning my OSE game The Golden Heresy, that the binary setup that Old School Essentials through hit points didn't serve my purpose. Characters who are either ready to rock (at any hp total other than 0) or dead, just don't serve my aims. I want combat to leave a mark on a character. So this is a prime rule to alter or expand.

I also noted that the OSE's NPC reaction table doesn't really create a space for treachery and double-dealing in the way I like. It might be a hack worth considering as well.

Some Rules Have Hidden Functions 

Before hacking anything, have a long look at how this rule affects the play experience. Most rules in a really well-designed and honed TTRPG like Old School Essentials serve multiple purposes. Knowing how the rule works is not the same as understanding what the rule does. 

Take Morale as an example: On it's face, Morale is a system that serves to determine whan a monster runs away. In reality, morale serves two other major functions. First, it speeds up combat. Players don't have to kill everything in the room: After a few rounds, if they have been clever, the fight can end with a solid rout. It also creates a different culture of play: Players are more likely to run away if they see that players will do the same, encouraging players to be survival-oriented. And it creates a culture where cold-blooded murder is not a part of the everyday life of the player character. Where they have to deal with the moral dilemma of taking prisoners, or to negotiate surrenders. Which in turn, helps them think of monsters as a potential source of information, encouraging them to look for intelligence and advantages everywhere. If you were to remove morale, as they did in Third Edition, the game becomes far more combat heavy. Players focus more on becoming murder machines, and less on being strategists and explorers, in general.

 it is good to double-check what a rule does for the game as well as what it is on its surface. It can help you decide how to modify it, or whether to modify it at all. In the case of morale, eliminating it altogether creates a very bloody game. And a frustrating one, if it doesn't have very tough player characters. On the other hand, making monsters more likely to run away or surrender might entice players to be more aggressive. Neither of which suit my idea very well. I would probably choose not to hack it on that basis.

Looking for Gaps

Often with game rules, less really is more. If you don't have anything noted on the character sheet, a player is more likely to experiment with what is possible. For example, if you have a list of skills or feats on your character sheet, a player character might never attempt something they don't have a skill or a feat to cover. In a game with no skill system, player characters will instead ask if they can attempt something, and come up with a good justification for why their character might be able to pull it off.

That said, sometimes your campaign will need something that the base game system won't offer. If there are things that the rules don't cover that you think they should, now is the time to figure out how to create, or steal rules that do the job.

In the first adventure I have planned for The Golden Heresy, the PCs are roaming an atomic wasteland. If all goes well, this adventure ends in them finding a portal to a more traditional D&D fantasy world that they have the noble task of wrecking. If not, this campaign becomes a story about survival in a nuclear wasteland until they can escape back into the Vortex. I wanted to make sure that this game was full of disease, radiation, and mutations. None of which are handy in the baseline Old School Essentials books... 

...But there are plenty of places where such rules exist. I decided to steal a very basic radiation rule from the video game Fallout 4: damage done by a radiatioactive source cannot be healed until the radiation is purged. This fills a critical gap for the experience I want to offer.

Pre-built Hacks! 

It bears mentioning that some TTRPGs on the market are designed only to be a replacement set of Subsystems, rather than a whole game itself. Pacts & Blades, for example, offers a frenzied combat system and Moorcock-inspied Pact Magic system that can be superimposed over any other TTRPG. As was Jason Vey's Age of Conan magic and combat system for OD&D.

Currently he O5R movement - people who are striving to create Hacks for Dungeons & Dragons 5e to make it feel more like a classic OSR experience - have put out a few amazing rules collections like this. Hankerin Ferinale's 5e Hardcore Mode and Gryphglyph's Darker Dungeons come to mind immediately.

Some other TTRPGs, like The Black Hack, are essentially a catalogue of innovative house rules for OSR games that you can pick and choose from. The Black Hack is built on a B/X skeleton, and so any or all of the rules in it can easily be ported to any other OSR game. Index Card RPG Core 2e is another great example of this; it is a total rewrite of D&D5e to use the best rules from the OSR, indie, and GLOG communities.

How to Hack

Be Transparent!

The first rule of hacking game rules is to be transparent. Rules exist for TTRPGs to narrow the game into one particular sort of experience, and to make sure that the game is fair. You know the rules, and so do the players. Even when the rules say a GM can cheat, it still is a rule, and usually offers parameters as to when and how the GM should cheat. This breaks down if the players aren't permitted to understand the rules of the game that they are playing. Every modification and house ruling ought to be pointed out to the PCs.

Some GMs are not comfortable with the idea of having a metagame discussion at the table, especially if it has to be done during the flow of play. But as you explain your rulings, you will find you get a lot more buy-in and trust from your players to be fair.

Keep a Reference

One of the best practices when modifying a game system is to keep a document that contains a description of each of your house rules and modifications. It helps if you keep notes on how and when it got used, and what the effect was on gameplay.

For many years, I kept my house rules and home-brew content in a purple duo-tang that traveled with my rulebooks. And when I wrote a campaign primer for my players, I included a list of all the home rules that I intend to use in the campaign from the outset.

Nowadays, a duo-tang is not necessary; mobile devices and cloud computing means that you can access and, for transparency, share your rules notes with players as you see fit. A Google doc, or a Google drive folder full of documents will do the job nicely.

Stealing from a Similar Source

One of the easiest ways to modify or hack the rules of a game system is to steal them from a game that has a similar engine under the hood. This is one of the reasons that d20, OSR, and other open game systems like Into the Odd, Forged in the Dark, Open d6, Powered by the Apocalypse, Fate, Fudge, and Gumshoe are mainstays of TTRPG design. Once someone has built a game based on one of these engines, any innovative rules or mechanics they include can be easily lifted and plugged into another game made with the same engine. If someone creates an interesting PbtA mechanic, like the Last Breath move in Dungeon World, it can be plugged into any PbtA game with almost no effort.

This is a place where the OSR really shines. There are dozens of retroclones built on B/X D&D or AD&D (which are pretty intercompatible) or d20. It is often very easy to take parts out of one of these systems and put into another without a great deal of trouble.

Going back to the example of my Golden Heresy Campaign setting: Aside from radiation, in order to grab that Atomic Pulp feel, I also want to have a table of horrible mutations a PC can develop from exposure to magic, radiation, and bio-agents in the wateland. It will take very little effort to steal mutation table from The Wasted Hack, because it shares the same B/X DNA as OSE, and based its mutation mechanics from Gamma World, which was originally built on an OD&D shell, itself.

Likewise, to keep fighters interesting in my home game setting of AEr, I have adapted the awesome Mighty Deeds of Arms mechanics from Dungeon Crawl Classics RPG. This system is so simple that as long as the game works on the same basic assumptions about Melee combat as Dungeons & Dragons, it takes very little effort to make it work.

When hacking a subsystem from a game with a very similar engine, there is not much to consider so long as the games use a similar Bounded accuracy. That is to say, the scale of their numbers are pretty close together. If the dice and bonuses are too small or too big for the system you are plugging them in to, try to look at what are rough equivalents and use that to make the numbers match your system.

For example, when I was porting Mighty Deeds of Arms into a B/X clone, I had to look very carefully at the impact of the deed die on attack and damage. A Fighter in B/X gets a 5% better chance to hit at every level from 1-10. A 2nd level fighter has a 10% better chance than a normal mortal man to hit the same target. A 5th level fighter a 25% better chance. In DCC RPG, however, they replace that bonus altogether with a random die roll. a 1st level Warrior or Dwarf can get anywhere from a +5% to a +15%... which isn't too bad, but a 5th level Warrior or Dwarf is looking at anywhere from a +5% to a +50%. It gets really swingy, and can make a character hit things they would not be able to hit otherwise. I was tempted to keep it as is, but decided that for my needs, the Deed die probably just should not impact attacks, keeping to a standard +5% per level base attack bonus.

Abstract the Subsystem

Let's say, for the sake of argument, that you are thinking of instead porting a mechanic from a radically different system. The thing to do is to remind yourself that a perfect one-to-one translation is not possible, and probably not even desirable.

Instead, your goal is to create a rule in your game of choice that captures the spirit of that rule.

And so the first step is to express the rule you want to steal for your game at its most basic form. Describe it without any reference to the actual dice or mechanics that the game uses.

I am going to do an extremely detailed version of this in a couple of article's time, but I want to do a simple example here. So let's work with the Last Breath mechanic for Dungeon World.

For arguments sake, let's imagine I am writing a game about playing Cthulhu Cultists using the Forged in the Dark engine that powers Blades in the Dark. And I really want Last Breath in there. Let's take a look at Last Breath's mechanics:

Last Breath

When you’re dying you catch a glimpse of what lies beyond The Black Gates of Death’s Kingdom (the GM will describe it). Then roll (just roll, +nothing).

• On a 10+, you’ve cheated Death —you’re in a bad spot but you’re still alive.
• On a 7–9, Death himself will offer you a bargain. Take it and stabilize or refuse and pass beyond the Black Gates into whatever fate awaits you.
• On 6-, your fate is sealed. You’re marked as Death’s own and you’ll cross the threshold soon. The GM will tell you when.

The Last Breath is that moment standing between life and death. Time stands still as Death appears to claim the living for his own. Even those who do not pass beyond the Black Gates catch a glimpse of the other side and what might await them—friends and enemies past, rewards or punishment for acts in life or other, stranger vistas. All are changed in some way by this moment—even those who escape.

The key thing to remember is that a brush with death, succeed or fail, is a significant moment that should always lead to change.

("Last Breath" is From Dungeon World: CC-BY-3.0, Sage LaTorra and Adam Koebel) 

So, lets break it down. If your character is mortally wounded, they get to see the other side. Then a test is made with three possible outcomes. The best possible outcome is that they PC is just unconscious, but will live. The next best outcome is that an otherworldly spirit offers to save their life in return for a favour. The worst outcome is that the character just dies. Nothing like the character's constitution matters for this roll.

It never hurts to look at the math, either. So the best possible outcome, survival, has a 2 in 12 chance of happening. The next best outcome, a Faustian bargain has a 5 in 12 chance of happening, as does the odds of just plain dying.

This actually works really well in Blades in the Dark, because it also has a graduated success system. It has a great success, partial success, and fail mechanic with slightly different odds. Getting the best possible success even has the same chance, although the PCs are slightly less likely to get a partial success.

If I am happy with the slight shift in odds towards death (50% vs. 42%), then importing Last Breath into Forged in the Dark is dead easy. I might add some stress to the character, as Forged in the Dark has valuable tools for describing the effects of Trauma that are absent in Dungeon World.

Aim for (Reasonable) Unity

Because you cannot hope for a perfect translation of a mechanic from one game to another, your goal here is to make a rule that works in your system. Ideally, you want to find ways to make it work with the rules and mechanics that already exist in your game.

If I wanted to port Last Breath into an AD&D retroclone, for example, I might try using Save vs. Death Ray as my way of using Last breath when characters hit 0hp. On a fail, they die. On a success they are offered a bargain. On a natural 19 or 20 they are at 1hp and unconcious. This skews the math even farther (60-65% chance of death at 1st level), but makes high-level characters more likely to be offered the Bargain.

It is not a perfect translation of the Dungeon World mechanic, by any stretch of the imagination, but D&D players understand, and are comfortable making a Save vs. Death Ray.  It does not need to add much to the rules.

I do believe that unified mechanics are not necessary to make a good role-playing game. A slightly Kludgy system that plays right at your table is a far superior to a system that is seamless, but forced. This is a judgment call; in many cases you can just roll as if you were using the rules' original system. Thee is absolutely nothing wrong with just asking a player to roll 2d6 when his character hits 0hp.  It is might be a bit inelegant, but it is also dead simple, and cuts down on mental gymnastics.

Hacking Ahead of Play

The vast majority of the rule-hacking you are doing is probably going to happen as your are building your campaign notes before the first session. It is a good idea is to both put it into any campaign primers or other material you are going to offer players, and to keep a set of notes on how it is working for you in the journal, keep an eye on how it plays out in practice, in case you need to make additional adjustments.

Hacking on the Fly

I have found myself needing to make new subsystems for the game that I am running in the middle of play. My primary example is the creation of a flashback mechanic based on the one in Blades in the Dark to use in Index Card RPG Core 2e, which I will cover in detail in a few articles, but others have also arisen. For example, I have needed to come up with a set of effective mechanics for dealing with a sandstorm in Dungeons & Dragons 5e (I used a complex trap from Xanathar's Guide to Everything), rules for using bio-warfare in AD&D2e, drag racing involving mechanical sabotage in Changeling: the Dreaming, Castle construction in D&D3e, and Toboggan Chases in Teenage Mutant Ninja Turtles RPG... to name a few.

In each of these cases, I needed more than a single roll outcome, and I needed something that didn't have an obvious way to handle it in the system in question. Otherwise, I would just make a ruling and move on. In this case, your best weapon is something that you can steal from some other role-playing game.

There are three important things to do here for maximum effectiveness:

1. Remind yourself that you don't need perfect, you just need "good enough." You neither need the other rulebook on hand, or for it to fit perfectly with the game that you are playing right now.

2. Explain to your players that you are going to be borrowing rules from another source or making them up. Try to explain your thought process, if you can do it in two minutes or less.

3. Write it down and make notes on how it worked. It may be needed again.

So, in the case of my old TMNT toboggan chase, it went something like this:

I realized that none of the Palladium books in my collection had quick, hackable chase rules. I needed something on the fly. Also, I would be damned if I stole the rules from Shadowrun 2nd Edition for it... they were awful.

So I figured out that what I needed to do was make the chase take some time. I started with a magical, out-of-nowhere number 50. And I decided that the character steering the toboggan had to make  a PP test to keep up speed. If he succeeded, I would take his roll off the 50.

Each round they would run into 1d4-1d4 obstacles. The driver got to roll his dodge skill against one of them opposed to an attack roll of 1d20+5. If another came up, another player would have to sacrifice their turn to be the one to dodge. Otherwise the sled would crash and they would take 4d6 damage from eating snow and dirt, and the bad guys would get a free round to stop the sled, get out, and start shooting.

Anyone left (there were 4 on the toboggan) after obstacles were dealt with could make ranged attacks at an -4 penalty. BOOM! Done! So, once I had it figured out I scribbled it down and said:

"Okay guys, looks like you have a James Bond style Snow Chase. I am winging this one, so the rules are going to be funky. But I set a target number of 50. Mark is steering so, he has to roll under PP each round. If he succeeds we get closer to the bottom. If he fails, you are too busy swerving to make progress. I will also randomly generate some obstacles. Mark gets to Dodge one of them - I'll make the tree or whatever attack you. If you get hit, you crash; it'll hurt, and the bad guys get a couple of rounds to come shoot you. If there is more than one obstacle, someone has to give up their turn to roll dodge in order to push off it. Shooting from a sled is at a penalty. Cool?"

FWIW, I started rolling for the enemy toboggan, and after a few rounds the bad guys collided with a tree, and the PCs ran up and beat the rest into submission. Fun, but disappointingly short, actually.

Train Future GMs

This level of transparency does something really helpful; it demystifies the GMing process to players. It might take them a little out of immersion for a moment, but it also makes the job seem easier, more like improv and guesswork, and less like a science.  After the campaign, letting players look over your notes can be really helpful, too.

Some Cautions

Careful with Math!

Most TTRPGs are not as delicately balanced as you might thinmk, but any rule that significantly changes the numbers in the combat or task resolution system is going to give either the players or the villains a major advantage. The smaller the dice rolls, the bigger this impact is going to be.  Make sure, if you ate giving out bonuses and penalties, that they are equivalent to the numbers you are used to seeing in the game. A +5 bonus to anything is pretty typical in Pathfinder, but it will break D&D5e.

But Not Too Careful... 

That said, if you worry too much beyond asking yourself "does this look consistent with the numbers I am used to seeing for this system and level of play?" is going to make you spend a lot of time reverse-engineering or fussing. There is room for trial-and-error. Nothing needs to be perfect.

Simpler is Better

My toboggan ride rules are about as complicated as I would be willing to make. TTRPGs are prone to becoming needlessly complicated. And when they do players can be frustrated and play can slow down. Try not to make anything too dicey or add too uch to the character sheet.

Does This Serve Your Vision?

When you are contemplating a hack, take a moment and revisit your poster pitch and ask yourself: "Does this fit my genre or my campaign descriptions? Does this fit the experience that I want to create?" If it doesn't then you might want to consider whether it is worth the effort.

Get Feedback

Feedback is the breakfast of champions, and the favored snack of great GMs. The best way to understand whether your Hacks are serving their purpose is to get the players to tell you about their experience.

What Are Your Watch-words? 

Most people are notoriously bad at giving constructive feedback, unfortunately. If you want the best possible feedback, you need to know how to ask for it. This is a big article unto itself, and one I might tackle next month.

For now, I suggest you make a note of the qualities you most want to offer your players in the experience and treat them as your watchwords. Having three of them might be ideal. Here are some examples of good watch-words to consider:

Fast, Easy-to-understand, Challenging, Exciting, Engaging, Lore-rich, Tactical, Immersive...

These can change every few sessions or so, of course.

Once you know your watch-words, ask your players if they find that the game that you are running fits that description, and if there is anything you could change to make it more effective. It would sound like this:

"Hey, Kat, I am trying to hone my game. One thing I really want is for my game to feel Challenging to the Player. I want to make sure that you feel like the encounters in front of you make you think and want to come up with creative solutions. Do you think that the game is doing that for you? Is there anything you think I could tweak to make it more Challenging? [...] Thanks. Also, I really want the game to move Fast, because we are all so busy. Have you noticed anywhere where the game lags I might need to tighten up?"

You might need to ask a few more questions... and you may not get much, but take good feedback like it is solid gold, and tune your game to take the best advantage of it.