I had to ask this question at one point, so here it goes: How far can you go when designing a new combat system if you want to keep it compatible with D&D (and friends)? There are several important factors at work, not the least being to ask what will be accepted by the audience. And there's certainly a line which, when crossed, will result in something new, only related to D&D in a very abstract way. If this line is crossed, it needs to be done deliberately. What follows are my thoughts and observations regarding the problems a writer of a game might encounter.
What is compatibility?
On a very basic level, it's not so much the understanding of what has been changed in a new set of rules, but the access to comparable data that a new system offers. In other words, to see if something is compatible you don't need to know how combat works, you'll just take a look at the relevant stats and see if they correspond with what you know. So if there are still hit dice, hit points, armor class and a base attack (of sorts) and they all work within the parameters you know from some version of D&D, you could just take an adventure or monster written for the new system, use it with your own system and it would work without too much trouble. You needn't even know the new rules and that's exactly the point.
As long as a designer keeps within the information D&D is supposed to produce, he's relatively free to change how he gets there. To answer the question: compatibility is a shared set of information and values between systems, it's not how a system gets to produce that information and values.
But how is it still D&D if you change the procedures that make it D&D?
Yeah, this is a tricky one. What ideas represent D&D and make it the game it is. There's not much arguing about the specifics, as they are a matter of taste. But that, on the other hand, means that within what D&D could be, there's a lot of choice. Some might keep with the original product line, saying it's D&D because it says so on the cover. And even here you got a wide spectrum of choices, from those who claim that the first edition of the game is the only edition that fits the bill and those that say, the newest edition is truest iteration, since it's the end of a long (and still ongoing) process.
But you could focus on the system instead of the official product line and you would be well in the territory of clones and variants. Not the game by name, but, as you would read on a regular basis on OSR related blogs (but sure not exclusively), it's D&D in every other way. There is a tolerance how far that might go, but mostly it comes down to choosing a variant of D&D over another. The core system is in all cases still recognizable.
Another extreme in this plethora of choices could be those who play Dungeon World, rules-wise a completely different system with almost no connectors to any version of D&D, and claim that that's how D&D is supposed to be played. And they are, to some degree, right in saying so, as Dungeon World manages to emulate what could be called a D&D experience.
The examples above illustrate that it comes down to three major groups: Official D&D, variants of a D&D system (but not D&D by name) and the tropes/clichés/stereotypes originating in D&D but emulated in another system.
|This is D&D, for sure! [source]|
All those can be D&D or can make a game feel like D&D. But they also need to compliment each other. If you reduce one aspect, you need to emphasize another to stay within this framework. Official D&D would be allowed to introduce radical changes to the system (as they already did several times), but it would still be D&D by name and well within the framework. Variants may change the name and parts of the system, but it needs to be compatible to some version of original D&D to stay within in that framework. And if you get rid of the system, you need to keep the stereotypes associated with D&D emphasized or you might end up playing Apocalypse World instead of Dungeon World.
Change the system, the name and the stereotype and you got something like Runequest (to give but one example of a game that was clearly inspired by D&D but wanted to be it's own thing).
As long as the designer of a game is aware of those possibilities and how they interact, he will be able to say if his game is still D&D or not. Even more so, he can direct his design choices to make a game part of what could be considered D&D. There is that line I talked about above and if it's crossed, it results in a new game with only some of the DNA of D&D (which would be true for almost every other rpg out there, if I may say so). Being aware of that can only help when trying to tell people what the game you're writing is all about or why it is still D&D.
So, will Lost Songs of the Nibelungs still be D&D?
Short answer? I believe it is. Somewhat. My reasoning at least is. And the result will be compatible with other D&D systems, so there is that. But arguing my case would go far back to ideas formed in the very first edition of D&D (mostly the idea that you should make the game your own*) while working with assumptions introduced in the D&D Rules Cyclopedia, sprinkling it with AD&D and some 3e concepts, getting rid of character classes and radically changing combat procedures in the process (so far). So if I tried to make my case, I'd end up using more words than the definition might justify. But it is there. Will you be able to play it just by knowing D&D? Maybe not.
But you will be able to take what you want and use it in D&D or take parts of D&D variants and use it in LSotN (to some extent, at least). So I guess it stays in the family. If I were to describe it, I'd say it's an "OSR fueled D&D Frankenclone". The rest I'll find out when the chips are finally down.
|D&D, allowing house-ruling since 1974!|
Anyway, it is D&D combat and it is not ...
Now back to the original question: How far can you go when designing a new combat system if you want to keep it compatible? If you agree with my assumptions about compatibility at the beginning, we'll have the room within the rules we can navigate in and that is the procedures that produce and interact with the terms we learned to use when playing D&D (xp, to hit, hd, ac, all that). You'd expect a certain range for armor class and a way to find out if you've hit the target or not and what damage you made, which relates to hit dice and hit points within a range of levels, and so on. D&D normally uses a twenty sided die (results ranging from 1 to 20) as a key element in combat (it connects to-hit with ac and level/HD to regulate hit points) and is supported by dice variants for initiative and damage.
What I'm trying to achieve now in LSotN, is replacing the d20 with a roll of 3d6, fragmenting the d20 (so to say) and ending up with a system that, while still being in the range of the d20, allows a player to get initiative, defense, attack, damage and a selection of other actions with just one roll per round. The Bare-Knuckle Fighter and the Pub Brawl Expansion** showcase that it is possible and not only works, but also supports tactical thinking, planning and bluffing. But it still ends up producing the same results you need in D&D to interact with the stats presented in D&D.
I'm not saying here this is the only way to go or the philosopher's stone or anything like that, but I hope it shows that there is some room for game design between rolling to hit something and finding out if it happened, without changing the original assumptions that work for D&D. And I hope it helps a bit in understanding my thinking behind those dice mini-games I tend to write about so much the last few days.
In the end it's for you to decide if that's still D&D or if I went too far with this.
*I elaborate on this further in a post I wrote last year, but it would too far away from what I'm writing about here. The post can be found here.
**That link leads to a complete and detailed set of rules, a somewhat less detailed version would be The Bare-Knuckle Fighter without the expansion. It can be downloaded here. The game-sheet itself will have all the necessary rules, the introduction can be seen as a strategy guide for the game.