So let's talk about the hows and whys of hacking a TTRPG system as a follow-up to my articles on finding the right system for the TTRPG experience that you want to create and why you might still want to modify the rules. After I am done this article, I am going to give you a review of John Harper's masterful Blades in the Dark, and then I will go into fine detail about several rules hacks I have made borrowing ideas from it and plugging them into my standby: Index RPG Core 2e. Which will lead into the extreme version of rules hacking: building your own bespoke TTRPG.
Once I've done that, it is my hope that I can create an index of useful rules to hack and where to find them, as well as sharing another example of a hack in the form of the encumbrance system I created for my custom home rule set, AEr (previously discussed here and here).
So, Why not Play RAW?
Most TTRPGs are so deliberately open-ended and artfully vague that there really is no way to play "Rules as Written" to begin with. The Rules are there to provide a few mechanics to resolve problems, and expect that the GM will be able to extrapolate from those a fair way to adjudicate described layer actions. They can provide a frame, but no game system can even hope to be comprehensive.
Most of the more "crunchy" games out there offer they sheer volume of rules and content they do because they are trying to narrow the scope of the game to create on particular experience. For example: Dungeons & Dragons, as it was originally conceived, is a game about sneaking into mysterious and surreal labyrinths full of monsters to claim ancient treasures and magic powers. To make that work, they created specific rules, like experience points and levelling, designed o make players want to keep going back into the dungeon, and focus on getting treasure, not fighting monsters or seducing barmaids.
Gold for XP was one of the best ways to make this happen: Your character gets better faster if they steal gold; fighting monsters gives you a much smaller amount of the points necessary to get that level. If you didn't want to get your character killed and have to start over, you were best served by bringing your creativity into avoiding being caught by the monsters, and avoiding combat. A huge chunk of the structure of OD&D and AD&D was designed to serve that game play loop.
Levels, spell levels, gradated monster Hit Dice, improving character class abilities, character hit point increases; these all exist almost entirely to support that loop. All D&D actually needed to work is the Ability Score check, attack and damage rolls, and saving throws. And games like Into the Odd prove handily that D&D could still function as D&D with only one of those roll mechanics.
Where it isn't important to narrow the scope of the gameplay experience, TTRPG games generally remain as vague as possible. You honestly don't need an elaborate engine for seducing the barmaid, as it is not a particularly important part of the gameplay loop of D&D. If it is absolutely critical to the game's narrative to know whether or not the barmaid is seduced, (assuming she can be,) the GM can call for a CHA check, modified based on whatever circumstances he feels are appropriate. No more is needed. We don't even need to have a table of modifiers to say that there is a -2 penalty if she is dating someone casually, -4 if she is in a serious relationship, and -10 if she is married; those vagaries are something we trust to the GM's judgement.
And yet even if I were to decide the same barmaid from the same module is probably at -10 to seduce and the GM down the street from me thinks she can be seduced with Advantage, we are both playing to the same letter of the rules... because the letter of the rules doesn't actually give you a lot to work with.
And because it is left to the GM's judgement, no two games of Dungeons & Dragons will play exactly the same way. Brian's ... & Dragons will be very different than Stephen's Dungeons & Mostly Eldritch Nightmare Things, even if we are both playing out of The Dungeons and Dragons Rules Cyclopeadia.
It is worth noting that the two games that served as the testing ground for creating Dungeons and Dragons: E. Gary Gygax's Greyhawk and Dave Arenson's Blackmoor were not played according to the rules of Dungeons & Dragons per se. The rules that were published in 1974 were a simplified compromise between the various experimental ways they handled turning Chainmail into a an immersive high-narrative sword and Sorcery adventure game. Travis Miller over at Grumpy Wizard has a more comprehensive discussion on what was actually played in the early days at TSR.
TTRPGs are in essence, not much more that task-resolution systems with a varying level of granularity, and then a set of rules that complicate, expand, or create alternatives to that task-resolution system that really exist to Funnel players towards a specific experience and enhance that experience.
If you want something that approximates the experience that the game's designer had in mind, then playing RAW might get you somewhere in the same sports complex... although even the same ballpark might be asking a bit much. And you might want to play RAW if you have no clue what kind of gaming experience you want at all and are just grabbing a system because it is a favorite or looks interesting.
But if you want to relate something more to your taste, it pays to go over the rules, figure out what kind of experience they are providing, and see if you can modify them to be more in line with the experience that you would like to have.
Developing a Vision Statement
The first thing that I recommend before you break out the blowtorch and soldering iron is that you know what it is exactly that you want to create. What is the high concept of your campaign, so that you can make sure that your bespoke system can support that experience better.
This takes surprisingly little to do. I tend to create something I refer to as a "Poster Pitch" to entire my players to agree to the campaign. Generally speaking, I have so many ideas going on, I can hand three or four of these to my players at any given time and let them pick the one that most appeals to them. It creates a lot of buzz.
The Poster Pitch
The Poster Pitch is designed to contain as much information as a mid-1990s movie poster would include, give or take some details. Here's the basic steps:
1. Title: Give the Campaign a Working Title
2. Genre: Choose a genre. Genre may be an illusion, but it is a really convenient one for communicating what players can expect. The most populate genres that are easy to support are likely Superhero Stories, Sword & Sorcery, Space Opera, Cyberpunk, Urban Fantasy, Heist Story, Mystery, and Spy Thriller. Of course you can get as granular as you like, or mix genres together however you please. The point here is to be able to put a comprehensible label on your campaign that your players will understand.
3. Descriptors: Choose two adjectives that describe the feel or action that you want. For example: grimdark, swashbuckling, surreal, sexy, mysterious, cinematic, treacherous, or high-octane. This is where the meat of your work is: these two words.
4. Write a tagline: This is a sentence or two that gives a feel for what the players can expect. This can sound like an actual movie tag line (like the one from Alien and later Critters 3: "In Space Noone Can Hear You Scream.") or it can be one telling the players what they might do.
5. Ludography: Make a list of a few movies, books, TV shows, or songs that you are going to draw on for inspiration.
6. System: Now that you know what the game is about, pick the actual rule system you are going with.
Then put it altogether like this.
A [Descriptor] and [Descriptor] [Genre] Campaign for [System]
So here is an example of how I would pitch my Golden Heresy Setting:
The Golden Heresy
A Dark and Surreal Sword & Planet Campaign for Old-School Essentials
To be free of the False Gods, beautiful fantasy worlds must burn, and you are the ones with the Torch.
Books: Nine Princes in Amber by Roger Zelazny, Elric of Malnibone by Michale Moorcock, Deathstalker Rebellion by Simon R. Green
Television: Stargate: SG-1, Sliders, She-Ra (Netflix remake)
Movies: Pandora, Wizards, The Last Unicorn, The Last Starfighter, Legend
Music: "Vol. 4" - Black Sabbath, "Accident of Birth" - Bruce Dickinson, "Wish Upon a Blackstar" - Celldweller
I often will do the whole think up as a mock movie poster. I find Pinterest is an incredibly valuable resource: I tend to collect Art that inspires me which I can grab to create a visual expression of what I want in my campaign. (But sadly can't use on my blog and respect copyrights at the same time.)
The Poster Pitch is just one of several ways you can create a vision statement; The point of having some sort of vision for your campaign ahead of time is simple: You want to have something you can use as a rubric for whether or not a rule or set of rules are serving the needs of your campaign.
Whatever structure you choose, what you need to know first and foremost is what genre are you trying to emulate, what inspirations you are using to create your campaign world, and what are the most important watch words in creating the "feel" you are going for. They will be what you use to decide what Hacks are right for you.
In the above Pitch, I use the watch words Dark and Surreal. When I choose my hacks, I am going to have to ask myself: "Does this make the campaign feel Dark, or work against it?" Obviously, Rules that make PCs tougher need to be considered very carefully, in this situation. Likewise, Rules that focus on building greater realism won't serve my "Surreal" vibe.
Doing a Little Worldbuilding
Once you have a Poster Pitch it is much easier to build a starting location and your ideas for the first adventure of the campaign, And as you do those two tasks sometimes there might be events, character abilities, etc. that are not covered by standard rules. In that case, you already know about mechanics that you have to build.
In The Golden Heresy. I wanted to have the first adventure begin in a radioactive wasteland. I needed some good rules for radiation exposure and mutations. I hacked in radiation rules from the video game Fallout 4, and mutation rules that I have seen in few Gamma World-derived TTRPGs.
One thing that is worth noting when you are designing a campaign is that nothing needs to be set in stone from the beginning. Even the system can be changed if you are not creating the experience that you want. Do not feel like your Vision Statement locks you into anything. The plan never survives first contact with the enemy, after all.
Campaigns are an aggregate of the experience the GM tries to offer the PCs, and the experience the PCs create with their character choices and style of play. You will likely have to readjust any or all of these ideas once the players have made characters and played through the first adventure.
You may find that your players' character concepts encourage you to build custom rules to suit them.
Do I Need to Hack?
So, once you have a Vision Statement, the next question you need to ask is "How much, if at all, do I need to change this?"
The first step to evaluating the system is to ask yourself how it functions in play, and whether that holds up to the experience you are describing above. It helps to go over the basic pillars of play and ask how this game handles them, and whether that is what you are looking for. I would also assess the core play goal of the game and whether or not it is what you are aiming for.
Let's take my Golden Heresy campaign concept from above and go over Old School Essentials and how it handles the game, using the Pillars of Play that are generally listed for Dungeons &Dragons: Exploration, Role-Play, and Combat.
Exploration: OSE uses a tight, turn-based approach to exploration indoors, and a looser watch-based approach when exploring hexes. Both are built on a risk-and-reward system. Indoors, a character's light sources slowly deplete as they more around in 10-minute increments. Every few increments spent investigating and exploring have a chance of brining up wandering monsters on the party, that offer a lot of danger and little reward.
Because OSE focuses on careful management of resources, food, water, and light, along with party hit points create tension. Searching a room for treasure and secrets are going to increase a party's chance of bringing home treasure, and thus leveling up. Characters have to deal with mounting pressure of whether or not they can afford to try "one more room" before they turn around and head home. Wandering monsters and getting trapped alone in the dark in a strange place are key pressures driving the system.
Does this serve to make the game "Dark?" It can... If it works well. But food and lamp oil are easy to buy in excessive supply and simple carry. And a single character with infravision can still get a whole party trapped underground out. If I want the game to feel darker, it needs to, well... Have more darkness. Finding ways to turn up the pressure on the PCs to guard their resources will be important.
Does it serve the purpose of feeling "Surreal?" Most of what makes a story surreal is not so much how exploration happens as it is where characters explore. Is engine is sufficient for that, so long as there is flexibility to make the locations visited strange and wondrous.
Roleplaying: Old School Essentials handles roleplaying with a less-is-more approach. Aside from NPC reactions, and how reactions in the middle of the table make it possible for players to change the course of an encounter through careful role-playing choices, morale and loyalty are about the only game mechanics geared towards supporting role play. There is almost no other system in the structure of the game that can resolve social and counters or uncertainty in roleplaying except for Charisma checks.
Does this support a "Dark" playstyle? Ultimately, it does not support or fail to support a dark feeling campaign. The rules here are neutral. If we wanted to encourage the game to feel darker, we could easily skew the tables to encourage treachery and deceit. A Madness mechanic might also work, especially one that is quick to degrade and slow to recover.
How about supporting a surreal style of play? This is almost a trick question. Surreal is often about describing how everyday humans adapt and cope when experiencing the otherworldly. Sometimes, that includes people who lose their grip on reality and develop a dreamlike logic in their behaviour. This is certainly something that you can role-play with NPCs. But very dangerous to try and force on a player character. If anything, the best way to deal with surreal in roleplaying is to not offer many mechanics for it. Except possibly two build some kind of custom response table for creatures have a particularly alien nature. I modeled this to a degree with the killer drones.
Combat: combat in Old School Essentials, by default, is fast and bloody. Smart players only get involved in combat when they have stacked advantages for themselves. Going toe-to-toe even with weak monsters is a good way to lose characters. Encounters are rarely balanced. However, injury is relatively land. It is hand waved away with hit points and a character is fine and fully functional until they are ready to drop dead.
So is it "Dark"? A lot of people tend to think of combat as being much darker in old school roleplaying games. Certainly, it is faster and deadlier. It is not treated like a sport, and characters are not super heroic in their combat abilities. Characters die with relative ease, which is fairly dark. However, the binary state of hit points is a big problem. There is no sense that a character might be disfigured, permanently injured, or maimed in combat. You are either up and in full fighting trim, or you are dead. Scars and injuries are essentially window dressing. I do believe upping the stakes a notch by making death slightly less likely but horrible injuries very likely might suit my goals a little better
Is it "Surreal" the simple, turn-based format for OSE doesn't really make combat feel strange, unpredictable, or alien in any meaningful way. Part of the problem is that it is strictly regimented in two turns. An alternative initiative system that makes things more rapid fire, disorienting, and confusing might be ideal. Looking at initiative hacks may be to my benefit.
What About Core Play Loop? OSE's core gameplay Loop is fairly straightforward. Player characters listen to Rumours as to where treasure and opportunities might be found. They go to a dangerous place, attempt to fill their backpacks full of gold and coins and gemstones, and then return home. How successful they were on their tomb raiding or burglary expedition, measured in foes defeated in battle to a lesser extent, and how much treasure they brought home to a greater extent gives them a reward in character experience. Enough experience, and a character levels up, becoming tougher, better at their skills, gaining access to different sorts of magic, etc. Over time, as characters level up, it should be reflected in the status afforded the characters. However, it does not do a good job of representing this except using relatively underdeveloped Dominion mechanics at 9th level. However, the rate of lethality in the game means that a high-level character is something of a status symbol amongst actual players.
Does it support a "Dark" style of play? As it is, it's a game about greed and cunning, which could be considered dark. It certainly doesn't preclude a dark style of play. However, one of the key themes of my concept is that the player characters initially represent the forces of Chaos trying to overwhelm the forces of Law. As the campaign involved, and the initial player character party dies out, it will likely flip to a campaign about the forces of Law trying to hold at bay the massing legions of Chaos. Accordingly this must be the major gameplay loop. It requires a system of awarding experience for gaining ground for your side of this conflict. Thankfully, there are optional rules that cover this already to an extent. Story goal and roleplaying rewards. However, something more concrete might be helpful.
What about "Surreal?" Eric Holmes had a notion about dungeons that I think is quite relevant. The dungeon feels more like a journey into a subconscious dreamscape than a practical fortification. It is full of monsters that often don't fit together with inscrutable goals. The idea of the dungeon itself is surreal, and if well presented crawling it can be a surreal experience. Finding ways to make dungeons feel alive, intelligent, and hostile may be the key. I do believe that there are some underused rules that could be valuable here, like the possibility of doors left open slamming shut on their own, and random dungeon events like spoiling food or strange sounds. This could be cranked up a notch to make dungeons, or in my case, exploration of strange planets and ancient high-tech locations feel extremely surreal.
Once you have looked at how the game works and decided where it needs to be tweaked, if anywhere to support your desired experience, another thing to consider is the content of the game. What things are in there that might support or hold back your play style. This can include any option offered to the player characters or any resource available to the dungeon master. In Old School Essentials, I would look at character classes, monsters, magic items, and equipment. These items set the tone of the game. In other games this can be radically different. For example, in The Cypher System the selection of type, descriptor, and focus that builds the characters are what builds the world and determines what is in it. As does the list of random cyphers that may show up in a character's hands. Adding and subtracting to that list can change the game without needing to do massive hacks to the system.
Considering what you might want to import from another game, or from a favorite piece of media is an important part of the hacking process. As is considering what you might want to strike from the system. Certainly, removing all spells that restore the Dead to life doesn't require changing any rules, but definitely changes the overall tone of the game in a very dark direction.