(This is temporarily being published today. I don’t quite have this week’s prompt story ready, but I did have this. I’ll switch the two tomorrow.)
Last week I talked about how the basic rules, The Player’s Handbook, should not be taken as Gospel. I mentioned how all games of Dungeons & Dragons are homebrew to some extent, because it’s all about making calls in circumstances nobody could have prepared for.
But really, one of the greatest assets of the 5th edition of D&D is how malleable it is. I would hesitate to call the system simple, because I don’t think any table-top RPG could be called such. But what 5th edition does is it sets out a layer of rules that are easy to follow, and once you understand what all the layers are, you can do what you want with them.
The key thing about that is that you need to know what the layers are. If somebody were to ask me if they could make their own class rather than use one of the ones in the book, I would discourage them from that idea. Not because I don’t want them to be creative, but because I think that’s simply the wrong way to tackle it. The classes in 5e are each designed to have half a dozen (or more) subclasses once you hit level 3. Paladins choose their “Sacred Oath”, bards choose their “Bard College”, rangers choose their archetype, etc. (This is also why a campaign of everybody running the same class is totally viable, but that’s a tangent.) I think making a new class is the wrong mindset, because the existing classes are already made like templates with different skill trees. If you’ve got a cool idea, I bet there’s a way to purpose it as a homebrew subclass of a pre-existing cleric, or sorcerer for example. This will also save you a lot of trouble down the line, believe me.
If your player wants to invent a new race, it’s a little different. It’s not as complicated stat-wise, but it can be a little annoying for a dungeon master. If you’re the only Mantis-person in the world, that’s a strange thing to put into the narrative, and it will always be prevalent. It doesn’t matter if the stats of a Mantis race are just copied over from Elf, because the DM would have to implant Mantis-people into his world just to make it so your character isn’t out of place. (Making them exclusive to this one island nobody has ever heard of does not solve the problem, because you’re still the only one.) This particular point will be specific to the dungeon master, though. Matt Colville doesn’t really allow any exotic race like Tiefling in his campaign, even though it’s an official, valid race. (He’s not wrong. It’s his game to run, after all!) So while making a race for one specific player is annoying, it’s doable as long as the DM is okay with it.
But there are things that are totally reasonable to invent on your own, especially as a DM. Magic items, for example, are things I almost never take straight from the book. Typically, I think about it’s origin and what it’s purpose was, and then I make something based on that. Let’s say a traveling merchant did a favor for a wizard as he passed through town. As thanks, the wizard made him a ring that allows him to haggle for better prices when he sells this goods. If the party gets their hands on it, I would say they are better at persuasion checks when selling. Buying stuff is a whole different story. (But as compensation I’d give a more hefty chunk because it’s a specific circumstance, like +2 or +3 to those checks, rather than a simple +1 when haggling.) Presenting very specific tools to the players will often adapt their play-style accordingly, as something like this will naturally make the party (even more) prone to looting everything they can find from bodies and dungeons.
Literally anything in the book is subject to change as you see fit. Like the idea of throwing a vampire into your story, but your players are far too weak to handle it? Just change the stats to make him less threatening. Instead of getting into how you’d do that, I’ll just direct you to Matt Colville’s awesome, albeit lengthy, video about it.
I said this last week, and I’ll stress it again. You’re all coming to this table to have fun. Don’t let the rules stop that from happening. The rules are for optimization. You can pick and choose what rules you like because you want to maximize the enjoyment for the players. In fact, once you play this game enough and you know all the ins and outs, you can easily bend the rules to have more fun!