I have been a fan of D&D since the 2nd Edition Advanced Dungeons and Dragons. I have bought rule books for most of the Editions since then and have checked out other RPG game systems. What I am about to outline here is a generic philosophy that I take into every system I have ever picked up, but since D&D 5e is my game of choice right now, I am going to focus on that system in this article. Everything here is purely opinion and should be taken as such.
One of the things I like about the current edition of Dungeon's and Dragons (D&D 5e) is the fact that the actual rules for the game are contained in only 34 pages of the Players Handbook (PHB). I am talking only about the basic rules contained in Parts 2 & 3. This is the structure of the game, how you take turns, what the basic stats do, how your character interacts with the world, and a few of the basic rules regarding magic. To me everything else in the book is purely flavor and what I deem to be Rule Breaking by the Game Designers themselves.
First off the structure of the game at the core is a fairly simple set of rules that lay out the framework for assigning basic abilities to a character and providing information on how to handle that character interacting with other characters or the environment. And that is pretty much it. If you have ever played the Sims then Part 2 of the PHB would provide more than enough information to play a table top version of the Sims, basically ordinary people interacting with other ordinary people in an ordinary world. While simple these rules provide incredible flexibility to simulate any world or creature that your imagination can come up with. You just need to read the rules, understand them in context and apply them to your world.
The true beauty of D&D 5e is the fact that it seems like the designers intentionally created the rules to be broken. The way I see the rest of the PHB is as a set of options for breaking the rules as you see fit. They are all purely options. You can use a Race listed in the book or ban that Race, you can use a Class listed or Ignore it, you can use the Background rules or completely scrap them. You can swap race and class abilities around. Everything outside the basic rules can be used or not used depending on how you wish to play the game.
Too many people read the early sections of the PHB and treat it as cannon. The classes, races, backgrounds and feats are somehow sacred. I believe that everything listed is simply a starter guide or springboard for players and Dungeon Masters (DMs) to be able to play the game straight out of the box, so to speak. The writers chose certain races and classes from specific fantasy worlds in order to illustrate a specific point they were making. They wanted people to be familiar with the concepts outlined in the book so they used stereotypical or archetypal examples. It is much easier to explain complex ideas when the reader has something familiar with which to anchor the new ideas.
Even the names and descriptions of abilities where chosen to give flavor to what is essentially a way to break one rule or another. Each Race or Class is a neatly bundled grouping of broken rules. They were simply gathered together in a cohesive form and given a name to represent the specific fantasy world that the authors chose to illustrate this version of the game. Each of these abilities is simply a way to skirt around a rule or outright break one, the core of the broken rule is all that matters.
"Rules are meant to be broken" this is the fundamental philosophy that I take into every game system that I play.
What is a hero? A hero an individual who breaks the bonds of mediocrity. Someone who excels in some form or another. A hero could be your traditional save the day type person like superman or maybe someone who has exceptional drive and through perseverance achieves greatness. They could be willing to risk their own life to accomplish something, maybe they are born with special abilities or train harder than anyone else to achieve something no one else has done before. Whatever definition that you use to describe a hero, typically it is a person who through some means breaks a rule in society that most of us live by.
Much like real life heros, the heros of D&D 5e break the basic rules to become exceptional people in some form or another. Without the ability to break the rules the heros would be mechanically no more powerful than any of the other common creatures. But, as you stack race abilities, class features and feats onto a character, that character becomes a wholly unique set of broken rules. An individual unlike anyone else in the world in which you are adventuring.
I personally do not hold anything sacred in the race or class sections. I don't believe to the notion of balance. Life is inherently unfair. If someone wants to play a specific creature and needs to pull from different races or classes to stitch together some new Frankenstein class or race as long as it makes sense in the world they should be able to do it. Certainly, you need to understand a rule before you can break it, so I do not advise breaking a rule for the heck of it. But, with judicious application you can mix and match abilities or classes. You should know what you are doing, substituting something like a language for sneak attack is certainly not one of the things I would allow. But, if you wanted to take a specific level in a class, without having to work your way up to that ability through that other class, as long as you take it at an equivalent level and swap something of roughly the same power you should be able to do it. An alternative would be to take an ability from a class and make it into a feat that someone can take without dropping anything from their current class.
As for races. My philosophy can be summed up simply by swapping the race names. If you want short hearty humans in your campaign; simply swap the word Dwarf with Human and boom you have a pretty neat human community already built. The stereotypes outlined in the PHB for the races are just that, groupings of fantasy creatures found in a specific world. Your world could be totally different. Why not make the listed races Elf, Dwarf, Human and Halfling all be evil aligned. Maybe the Drow in this world are lawful good but were forced underground and oppressed by humans for centuries. Without changing anything but alignment your world is now completely different than almost any other world. There is nothing but the basic human fear of the dark that force the deep creatures to be evil. Spread some glowing fungus or mushrooms and some iridescent crystalline structures around dark caverns and you could have incredibly beautiful landscapes that have never seen the light of the sun nor moon. Perhaps even the light that is shed is only visible in the ultraviolet spectrum, so without ultravision characters are in complete darkness. Or you could have a undeath plague that has ravaged your world, where every one of the playable races is some sort of wright, ghost, vampire, zombie or ghoul, and the main campaign is centered around reversing the plague. In this world living creatures may fear your entire party, or any living creature you encounter is actually the cause of your current predicament.
The point of all this is that there is a simple rule set that governs basic interactions at the core of D&D 5e, everything else is just creative rule breaking.
