If you’re thinking of making your own RPG, you probably have an idea of what dice you want to use, what characteristics you want to model and how heroic you want the characters to be. Those are important to think about, but where do you go from there? Let’s look at some guiding principles that will help you make a system that flows.
RPG systems can get complex really quickly. When designing a system, you want to keep things as simple as you can while still keeping the level of function where you want it to be. There are a few tools that will help you to do this. The first and most obvious is the unified mechanic, if you want every interaction in the game to be handled by one set of rules. Once the players learn that set, they can do everything the game is designed to do. The main consideration is to keep things consistent so the players don’t have to look up how something is handled, they just know because they’ve learned the core mechanic. GMs will tolerate looking up material, but the more you can reduce the GM’s mental load – the more creative they can be.
Now think about how many individual steps you have in your mechanic. From the start of a round to the end of a round, count up how many dice rolls, equations, calculations and steps the players will have to slog through. Are all of them needed? Can you cut some of them out and still keep the same functionality? Is a slight reduction of function still enough to get you where you want to go? Your first answer is probably going to be that they’re all needed or that taking some of them away will take away some feature of the game you like. However, if you allow yourself to kill your darlings and reconnect the dots without them, you may just end up with a stronger system.
Do your numbers have to be so big? If characters have 10 hit points and most weapons do at least 5 damage, couldn’t you make it so that characters have 2 HP and weapons do 1 damage? If payers roll 1d20 and the average difficulty is 10, is there a difference if you reduced things to 1d6 and the average difficulty is 3? There very well could be a reason for the higher numbers, but try to reduce them if it’s practical.
The last thing to consider is your math. “Do you need all that math?” would be the obvious first question. Could you provide a non-math approximation of what you’re trying to accomplish? If that’s not practical, try to change the type of math you have to do. Mentally, not all math is equal. Comparing two numbers is about as simple as you can get. This means looking at a number and saying if it is more, equal or less. Adding small numbers is the second simplest math operation you can have. Subtracting small numbers is actually slightly harder for your brain. Multiplication and division are probably not acceptable in the middle of play, unless you’re doubling or halving numbers. Small changes here add up over the course of a game. As a player’s mind is taxed to do repeated equations, they’ll slowly tire and become less creative. The more load you have on them, the more they’ll just follow the most obvious path.
The other question about math to consider is when will the players have to do it? A player that is going to get a big payoff from the math will more happily crunch numbers or at least more happily reach for the calculator. If the math is for something mundane or even harmful to them, it’s going to impact their enjoyment of the game.
This doesn’t mean you have to have a rules-lite system. The emphasis here is reducing the number of steps that have to happen in each round and reducing the mental load of the players. Extra steps are often acceptable for special effects that add spice to the game, but happen only occasionally.
Now that you have your core mechanic, try to think of how many ways it can be used. Does the same system that you used for combat apply to social conflict? Could it be used in a survival situation? What about when computer-hacking? How does a doctor heal characters using the system? Can a character maintain a troop of minions with the system and still have turns go quickly? Try to push the boundaries and find exceptions. If you haven’t found them, you haven’t looked hard enough.
Once you find the exceptions, examine what’s causing them. Is it the lack of a rule, or the existence of a rule? Either way, try not to add a new rule or step – see if you can modify the existing rules to encompass the exception. Sometimes when you’re able to do this, you blow open a whole new set of things your game can do, so really go after this whenever you can.
Think about the steps and rules you currently have. Can they be expanded to cover circumstances that you didn’t originally intend them to? If you’re already play-testing, a way to get some feedback on this is to pay attention to when a player misuses or misapplies a rule. They’re making a connection you may not have been thinking of as being a good thing. The player obviously thinks it is, so can you adjust things to fit the rest of the game?
Next think about how the mechanic can be abused. Is there an exploit that will make a character unstoppable? This may not happen right away; it often does happen as the PCs gain experience. Is it a bad thing? Can the challenge be moved somewhere else so that the PC is still fun to play? If you are going to migrate the challenge, make sure it happens slowly and that the players and the GM know that this is the direction the game will move in. This is vital so the players don’t get blindsided by the change and not understand how to keep enjoying their characters.
If you can let a PC max out any stat of their choice and the game is still fun and challenging, you have a robust system. If you can give them any piece of equipment they want and it doesn’t break the game, you’re doing pretty good. If the PC can be unstoppable in one aspect, but still vulnerable in another, you’re on to something.
Whenever a player tries something that has no effect in-game, you have a problem. When a player wants to do flips into a fight and the system doesn’t handle that, there’s a hole between what the player wants to do and what the system can handle. When the player wants to jump on the back of a beast and stab it in the neck, and nothing special happens, there’s a problem. When the player wants to start off with a horse and is willing to sacrifice other things for it, but they can’t, there’s a problem. Let them know how the change could effect the game and ask them for input on how the issue could be handled. It may require a lot of rethinking, but you’ll have happier players for it.